arm: Fix some bugs in the aapcs64 implementation.

arm: Fix some bugs in the aapcs64 implementation.

The templates which checked for short vectors, and our approximation of
HFA, HVA and HXA types were not correct. This change actually simplifies
them along with getting them to produce correct results. In the case of
HXA, there was a logic bug where an && was used where an || was
intended.

There may still be bugs in the actual collection of arguments and
setting of return values since those aspects are harder to test.

Change-Id: Ice3177205a98c678ecb43ba600813b3909c44e6b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/28267
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>