Use SV48 when possible #942

Job	Run time
riscv-arch-test	0s
jtag-dtm-test (freechips.rocketchip.system.WithJtagDTMSystem_freechips.rocketchip.system.DefaultC...	24m 59s
riscv-tests (DefaultConfig)	23m 6s
jtag-dtm-test (freechips.rocketchip.system.WithJtagDTMSystem_freechips.rocketchip.system.DefaultR...	22m 48s
jtag-dtm-test (freechips.rocketchip.system.WithJtagDTMSystem_freechips.rocketchip.system.WithDebu...	21m 7s
riscv-tests (DefaultBufferlessConfig)	23m 30s
emulator (DefaultSmallConfig)	15m 48s
jtag-dtm-test (freechips.rocketchip.system.WithJtagDTMSystem_freechips.rocketchip.system.WithDebu...	20m 19s
riscv-tests (DefaultRV32Config)	23m 39s
emulator (DualBankConfig)	16m 23s
emulator (DualChannelConfig)	16m 3s
riscv-tests (TinyConfig)	16m 56s
emulator (DualChannelDualBankConfig)	16m 41s
riscv-tests (DefaultFP16Config)	16m 59s
emulator (RoccExampleConfig)	16m 1s
emulator (Edge128BitConfig)	16m 1s
emulator (Edge32BitConfig)	16m 8s
emulator (QuadChannelBenchmarkConfig)	16m 21s
emulator (EightChannelConfig)	16m 49s
emulator (DualCoreConfig)	16m 14s
emulator (MemPortOnlyConfig)	15m 44s
emulator (MMIOPortOnlyConfig)	15m 51s
emulator (CloneTileConfig)	18m 7s
emulator (HypervisorConfig)	16m 2s
	7h 1m 36s

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