arch-gcn3: Update LmReqsInPipe in atomic flats when execMask=0

arch-gcn3: Update LmReqsInPipe in atomic flats when execMask=0

In flat instructions, wrLmReqsInPipe/rdLmReqsInPipe are decremented
in the calcAddr() function. However, the calcAddr() function is only
called when execMask != 0.

This patch adds in statements to decrement wrLmReqsInPipe and
rdLmReqsInPipe in all implemented atomic flats when execMask is 0.

This fixes a scenario where vector local memory and flat instructions
are unable to execute due to LocalMemPipeline::isLMReqFIFOWrRdy
always returning false in ScheduleStage::dispatchReady after too many
atomic flats execute with execMask = 0

Change-Id: I081cfd3faf74bbfcf0728445e7160fa2a76a6a7e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32614
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Reviewed-by: Alexandru Duțu <alexandru.dutu@amd.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>