arch,cpu: Get rid of ISA_HAS_CC_REGS and its associated ifdefs.

arch,cpu: Get rid of ISA_HAS_CC_REGS and its associated ifdefs.

This conditional compilation was unnecessary and makes gem5 more
brittle and harder to understand.

Change-Id: I63abaf2668252c988cdd4626ff6a462eb6f54b04
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/22544
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>