arch-arm,cpu: Replace rename modes with split reg/elem register files.

This simplifies the O3 CPU, and removes special cases around how vector
registers are handled. Now ARM is responsible for maintaining its
different register personalities internally.

Also, this re-establishes the invariant that registers are indexed as
complete, opaque entities with no internal structure, at least as far as
the CPU is concerned.

To make sure the KVM CPU sees the correct state, we need to sync over
the vector registers if we're in 32 bit mode when moving state to or
from gem5's ThreadContext.

Change-Id: I36416d609310ae0bc50c18809f5d9e19bfbb4d37
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49147
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
19 files changed