i965/fs: Simplify texture destination fixups
There are a few different fixups that we have to do for texture
destinations that re-arrange channels, fix hardware vs. API mismatches, or
just shrink the result to fit in the NIR destination. These were all being
done in a somewhat haphazard manner. This commit replaces all of the
shuffling with a single LOAD_PAYLOAD operation at the end and makes it much
easier to insert fixups between the texture instruction itself and the
LOAD_PAYLOAD.
Shader-db results on Haswell:
total instructions in shared programs: 6227035 -> 6226669 (-0.01%)
instructions in affected programs: 19119 -> 18753 (-1.91%)
helped: 85
HURT: 0
total cycles in shared programs:
56491626 ->
56476126 (-0.03%)
cycles in affected programs: 672420 -> 656920 (-2.31%)
helped: 92
HURT: 42