arch,sim: Use the guest ABI mechanism with pseudo instructions.

arch,sim: Use the guest ABI mechanism with pseudo instructions.

Right now, there are only two places which call the pseudoInst function
directly, the ARM KVM CPU and the generic mmapped IPR. These two
callers currently use the generic "PseudoInstABI" which is just a
wrapper around the existing getArgument function.

In the future, this getArgument function will be disolved, and the
PseudoInstABI will be defined for each ABI. Since it currently mimics
the Linux ABI since gem5 can only handle one ABI at a time right now,
this implementation will probably be shared by linux system calls,
except that the pseudo inst implementation will eat return values since
those are returned through other means when the pseudo inst is based on
magic address ranges.

Jira Issue: https://gem5.atlassian.net/browse/GEM5-187

Change-Id: Ied97e4a968795158873e492289a1058c8e4e411b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23178
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>