This is to fix incorrect VGPR spill placement with fastregalloc.
If SGPR spills were inserted in the first regalloc run used for the
exec mask, these instructions would break the block prolog. The
second regalloc run would then incorrectly insert VGPR spills before
the point where exec was setup.
Fixes #61083
Is this reordering fixing the bug mentioned in the description?
(Exec mask is restored before buffer_load, rather than after.)