When texture buffers are used as images in compute shaders, the guest
never sees the modified data since the TBO is always marked as clean.

Fixes most dEQP-GLES31.functional.image_load_store.buffer.* tests.

Example test cases:
   dEQP-GLES31.functional.image_load_store.buffer.load_store.r32ui
   dEQP-GLES31.functional.image_load_store.buffer.qualifiers.coherent_r32f
   dEQP-GLES31.functional.image_load_store.buffer.format_reinterpret.rgba8_rgba8ui

Note: virglrenderer side patch also needed to bind TBOs correctly

Change-Id: Ic58783f83b0a0702747197ec7d01d079e25cb09f