glamor: Fix x2r10g10b10, allow acceleration for more RENDER formats
Patch 1 fixes x2r10g10b10 related rendercheck failures.1
Patch 2 allows HW acceleration for more RENDER formats, as long as the constraint from patch 1 holds true.
Patch 3 removes an unused helper function I noticed while working on the other patches.
When running rendercheck manually; the x2r10g10b10 failures can still occur when rendercheck is run via piglit for some reason.