i965: Lift some restrictions on dma_buf EGLImages

i965: Lift some restrictions on dma_buf EGLImages

Allow glEGLImageTargetRenderbufferStorageOES and
glEGLImageTargetTexture2DOES for dma_buf EGLImages if the image is
a single RGBA8 unorm plane. This is safe, despite fast color clears,
because i965 disables allocation of auxiliary buffers for EGLImages.

Chrome OS needs this, because its compositor uses dma_buf EGLImages for
its scanout buffers.

Testing:
  - Tested on Ivybridge Chromebook Pixel with WebGL Aquarium and
    YouTube.
  - No Piglit regressions on Broadwell with `piglit run -p gbm
    tests/quick.py`, with my Piglit patches that update the
    EGL_EXT_image_dma_buf_import tests.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>