glsl: Lower shader storage buffer object loads to GLSL IR instrinsics

glsl: Lower shader storage buffer object loads to GLSL IR instrinsics

Extend the existing lower_ubo_reference pass to also detect SSBO loads
and lower them to __intrinsic_load_ssbo intrinsics.

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>