i965: Don't calculate masks of used FS inputs

i965: Don't calculate masks of used FS inputs

This previously enabled some optimizations in the fragment shader
(interpolation, etc.) if some input components were always 0.0 or
1.0.  However, this data was generated by analyzing Mesa IR.  The
next patch in this series removes generation of Mesa IR for GLSL
paths.  When we detect that case, just set the used mask to ~0 and
circumvent the optimizations.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>