arch-arm: Add missing isFirstMicroop flags on uop sequences

arch-arm: Add missing isFirstMicroop flags on uop sequences

Certain micro-op sequences were only setting isLastMicroop flags,
and did not set the isFirstMicroop flag. This adds the missing
setFirstMicroop() calls. This fixes tracing issues (e.g. Tarmac)
of certain micro-opped instruction sequences such as LD1.

Change-Id: I7de3ee2759e2b4e1065a7cbac4186f11227d84be
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/30034
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>