CpuExceptionHandlerLib: Added PcdSerialUseMmio condition. #484

Job	Run time
Linux CLANGDWARF	26m 55s
macOS XCODE5	18m 29s
Windows VS2019	31m 1s
Linux CLANGPDB	22m 16s
Linux GCC	18m 16s
Test (Ovmf, Ia32,X64,3264, XCODE5, RELEASE,DEBUG,NOOPT)	8m 18s
Test (Ovmf, Ia32,X64,3264, VS2019, RELEASE,DEBUG,NOOPT)	8m 42s
Test (Ovmf, Ia32,X64,3264, CLANGPDB, RELEASE,DEBUG,NOOPT)	9m 13s
Test (Ovmf, Ia32,X64,3264, CLANGDWARF, RELEASE,DEBUG,NOOPT)	8m 20s
Test (Ovmf, Ia32,X64,3264, GCC, RELEASE,DEBUG,NOOPT)	8m 17s
	2h 39m 47s

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