[AMDGPU] Mark GFX11 dual source blend export as strict-wqm

The instructions that generate the source of dual source blend export
should run in strict-wqm. That is if any lane in a quad is active,
we need to enable all four lanes of that quad to make the shuffling
operation before exporting to dual source blend target work correctly.

Differential Revision: https://reviews.llvm.org/D127981