iris: Resolve textures used by the program, not merely bound textures

iris: Resolve textures used by the program, not merely bound textures

st/mesa's PBO upload path binds a vertex shader that doesn't use any
textures, but leaves the existing sampler views bound in place.  This
was tricking us into thinking the PBO destination might be bound for
texturing in some cases.  In Civilization VI, this fixes a false self-
dependency issue that was preventing CCS_E compression on upload.
Fixing this slightly improves frame times.