arm: Use the common pseudoInst dispatch function.

arm: Use the common pseudoInst dispatch function.

Instead of manually calling each of the PseudoInst implementations, this
function will automatically pick up new instructions and greatly
simplifies the ARM ISA files.

Change-Id: I6cb94b3d115f50d681ca855f80f9d7d3df6bc470
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27791
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>