arch-arm: Fix tracing code for SVE gather

arch-arm: Fix tracing code for SVE gather

Printing the entire contents of the dest vecreg for each gather
microop is suboptimal as it creates false positive differences
between Atomic and O3 traces. This fix prints only the memory
data which a microop loads from memory.

Change-Id: Idd8e0b26a96f9c9cc0b69360174bedf6a9f6dcb5
Signed-off-by: Gabor Dozsa <gabor.dozsa@arm.com>
Reviewed-by: Giacomo Gabrielli <giacomo.gabrielli@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19171
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>