mesa: Get rid of texture-dependent image unit derived state.

mesa: Get rid of texture-dependent image unit derived state.

The point is to avoid having to re-validate all image units when
_NEW_TEXTURE is flagged, which can be expensive if the driver exposes
a large number of image units.  This has been reported to fix a 36%
performance regression in the Synmark2 Multithread benchmark on the
i965 driver which exposes 192 image units.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91788
Reported-by: Wendy Wang <wendy.wang@intel.com>
Tested-by: Ye Tian <yex.tian@intel.com>
CC: "11.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>