i965: Disable aux buffers for EGLImage-backed miptrees

i965: Disable aux buffers for EGLImage-backed miptrees

EGL does not yet have extensions to manage the flushing and invalidating
of driver-internal aux buffers. So we must disable aux buffers of
dma_buf-backed EGLImages in order to safely render into them.

This patch is obviously needed for renderbufers. It's also needed for
textures because the user can attach the texture to a framebuffer and
because the driver sometimes renders to textures for internal reasons.

Testing:
  - Tested on Ivybridge Chromebook Pixel with WebGL Aquarium and
    YouTube.
  - No Piglit regressions on Broadwell with `piglit run -p gbm
    tests/quick.py`.

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