i915: Add XRGB8888 format to intel_screen_make_configs

i915: Add XRGB8888 format to intel_screen_make_configs

This is a copy of commit 536003c11e4cb1172c540932ce3cce06f03bf44e
except for i915.

Original log for the i965 commit follows:

 Some application, such as drm backend of weston, uses XRGB8888 config as
 default. i965 doesn't provide this format, but before commit 65c8965d,
 the drm platform of EGL takes ARGB8888 as XRGB8888. Now that commit
 65c8965d makes EGL recognize format correctly so weston won't start
 because it can't find XRGB8888. Add XRGB8888 format to i965 just as
 other drivers do.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Acked-by: Boyan Ding <boyan.j.ding@gmail.com>
Tested-by: Mark Janes <mark.a.janes@intel.com>