Revert "radeonsi: only set BC_OPTIMIZE_DISABLE when necessary"

Revert "radeonsi: only set BC_OPTIMIZE_DISABLE when necessary"

This reverts commit 0543630d0b0d9d9f6eefbc14fbd3385d4de37ba0.

It caused flickering artifacts in Steam games such as Team Fortress 2 or
Left 4 Dead 2.

We could probably only enable this optimization by also making sure the
shader code only uses either SI_PARAM_LINEAR_CENTROID or
SI_PARAM_LINEAR_CENTER, not both. This would probably require a shader
variant.

Sorry I didn't remember this when reviewing the reverted change.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>