intel: Don't expose XRGB8888 visuals any more

intel: Don't expose XRGB8888 visuals any more

There really isn't any point.  There is no resource savings, and we have
to do gymnastics in the driver to make it work.

There are also bad interactions with multisampling and OpenGL ES 3.0.
In ES3, a multisample-to-singlesample blit must have identical source
and destination format.  This means a multisample RGBA8 to singlesample
RGB8 (window) blit will generate an error.  Also in ES3, RGB8 is not a
renderable format.  This means that the application CANNOT make an RGB8
multisample renderbuffer.

As a result, if an application gets an RGB8 window and wants to do
multisample FBO rendering, it will probably break.

"Fixes" gles3conform
framebuffer_blit_functionality_multisampled_to_singlesampled_blit test
on RGB8 visuals.

v2: Fix 'formats' array size.  Suggested by Ken.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Eric Anholt <eric@anholt.net>