intel: Only stall after sending all memory fence messages

Merged Caio Oliveira requested to merge cmarcelo/mesa:r/brw-pipelined-fences into master

In Gen11+, when emitting a fence for both L3 and SLM, instead of

SEND, MOV (for stall), SEND, MOV (for stall)


SEND, SEND, MOV (for stall), MOV (for stall)

This MR is on top of !3226 (merged).

Edited by Caio Oliveira

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