dri3, i915, i965: Add __DRI_IMAGE_FOURCC_SARGB8888

dri3, i915, i965: Add __DRI_IMAGE_FOURCC_SARGB8888

The __DRIimage createImageFromFds function takes a fourcc code, but there was
no fourcc code that match __DRI_IMAGE_FORMAT_SARGB8. This adds a define for
that format, adds a translation in DRI3 from __DRI_IMAGE_FORMAT_SARGB8 to
__DRI_IMAGE_FOURCC_SARGB8888 and then adds translations *back* to
__IMAGE_FORMAT_SARGB8 in both the i915 and i965 drivers.

I'll refrain from comments on whether I think having two separate sets of
format defines in dri_interface.h is a good idea or not...

Fixes piglit glx-tfp and glx-visuals-depth

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Eric Anholt <eric@anholt.net>