radeonsi: mark buffer texture range valid for shader images

radeonsi: mark buffer texture range valid for shader images

When a shader image view into a buffer texture can be written to, the buffer's
valid range must be updated, or subsequent transfers may incorrectly skip
synchronization.

This fixes a bug that was exposed in Xephyr by PBO acceleration for glReadPixels,
reported by Michel Dänzer.

Cc: Michel Dänzer <michel.daenzer@amd.com>
Cc: 12.0 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>