arch: Consolidate common debug flags.

Consolidate debug flags which are defined separately in multiple ISAs in
arch/SConscript instead. This will prevent conflicts when more than one
ISA can be compiled at a time.

Change-Id: I70862c403d19f04bbcbabd74dd751ca92d1ed942
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/50334
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

src/arch/SConscript

@@ -225,3 +225,7 @@ DebugFlag('CCRegs')
 DebugFlag('MiscRegs')
 CompoundFlag('Registers', [ 'IntRegs', 'FloatRegs', 'VecRegs', 'VecPredRegs',
                             'CCRegs', 'MiscRegs' ])
+
+DebugFlag('Decoder', "Decoder debug output")
+DebugFlag('Faults', "Information about faults, exceptions, interrupts, etc")
+DebugFlag('TLBVerbose')