mesa/glsl: new compiler option EmitNoIndirectSampler

mesa/glsl: new compiler option EmitNoIndirectSampler

Patch provides new compiler option for backend to force unroll loops
that have non-constant expression indexing on sampler arrays.

This makes sure that we can never end up with a shader that uses loop
induction variable as sampler array index but does not unroll because
of having too much instructions. This would not work without dynamic
indexing support.

v2: change option name as EmitNoIndirectSampler

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Cc: "10.5" and "10.6" <mesa-stable@lists.freedesktop.org>