i965: Validate (and resolve) all the bound textures.

i965: Validate (and resolve) all the bound textures.

BRW_MAX_TEX_UNIT is the static limit on the number of textures we
support per-stage, not in total.

Core's `Unit` array is sized by MAX_COMBINED_TEXTURE_IMAGE_UNITS, which
is significantly larger, and across the various shader stages, up to
ctx->Const.MaxCombinedTextureImageUnits elements of it may be actually
used.

Fixes invisible bad behavior in piglit's max-samplers test (although
this escalated to an assertion failure on HSW with texture_view, since
non-immutable textures only have _Format set by validation.)

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Cc: "9.2 10.0 10.1" <mesa-stable@lists.freedesktop.org>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>