glsl: teach std140_base_alignment about samplers
glsl: teach std140_base_alignment about samplers

These functions are about to be used more aggressively for determining
uniform layout. Samplers may be inside of structs, and it's easier to
reuse the existing base alignment logic.

Signed-off-by: Ilia Mirkin <bcbbb7aa705ec3a5fc5824c01a845186c3d62fca@alum.mit.edu>
Reviewed-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler