Fix some upload and test issues, especially for LPC1768

[multiplemonomials]

Summary of changes

I'm back to some of my old tricks, trying to set up a more permanent testing system for some of the Mbed boards. I'll provide more details later, but while doing this, I ran into some misc issues uploading and debugging code, especially (for now) on LPC1768.

Impact of changes

• Fix incorrect compilation of two tests (mbedtls-selftest and device_key-functionality) for targets that don't support them
• Improve USB test suite setup docs for Linux (including removing a usermod command that soft bricked my single board computer!)
• Add NOLOAD to some non-loaded LPC1768 linker script sections so GDB doesn't try to load them (which was causing OpenOCD to bail out due to incorrect alignment of a load operation)
• Update LPC1768 OpenOCD script to remove "gdb_memory_map disable", which was causing load to fail when executed by GDB. Now, we actually fix the problematic flash bank by disabling autoprobing for it.
• Don't pass --skip-reset to the test runner for devices which support semihosting and must be reset after code is loaded
• Use tbreak instead of break in GDB startup scripts so we don't permanently use 1 breakpoint on main()
• Disable GDB server when flashing with OpenOCD, I think this was causing problems when running two OpenOCD flash processes at the same time since they tried to bind to the same port
• Try to better handle semihosting interrupts in OpenOCD GDB (though I still can't get it to actually debug lpc1768 correctly without disabling the semihosting feature)
• Add tools/requirements-ci-build.apt.txt for installing build requirements with apt-get

Migration actions required

Documentation

None

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Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[X] Tests / results supplied as part of this PR

Test run for LPC1768:

97% tests passed, 3 tests failed out of 100

Total Test time (real) = 2816.05 sec

The following tests did not run:
          8 - test-mbed-drivers-lp-ticker (Skipped)
          9 - test-mbed-drivers-lp-timeout (Skipped)
         10 - test-mbed-drivers-lp-timer (Skipped)
         11 - test-mbed-drivers-mem-trace (Skipped)
         27 - test-mbed-hal-crc (Skipped)
         30 - test-mbed-hal-lp-ticker (Skipped)
         33 - test-mbed-hal-ospi (Skipped)
         35 - test-mbed-hal-qspi (Skipped)
         46 - test-mbed-hal-trng (Skipped)
         51 - test-mbed-hal-verify-arduino-pinmap (Skipped)
         62 - test-mbed-platform-crash-reporting (Skipped)
         72 - test-mbed-platform-stats-cpu (Skipped)
         73 - test-mbed-platform-stats-heap (Skipped)
         74 - test-mbed-platform-stats-sys (Skipped)
         75 - test-mbed-platform-stats-thread (Skipped)
         91 - test-mbed-connectivity-mbedtls-sanity (Skipped)
         92 - test-mbed-connectivity-mbedtls-selftest (Skipped)
         93 - test-mbed-connectivity-nfc-eeprom (Skipped)
         95 - test-mbed-connectivity-netsocket-nidd (Skipped)
        100 - test-mbed-device_key-functionality (Skipped)

The following tests FAILED:
         24 - test-mbed-usb-device-serial (Failed)
         32 - test-mbed-hal-mpu (Failed)
         97 - test-mbed-connectivity-netsocket-tls (Failed)
Errors while running CTest

I'm pushing one additional commit to disable connectivity-netsocket-tls for devices without TRNG where it won't build

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Reviewers

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