i965: Add real support for texturing/rendering with MESA_FORMAT_RGBA8888_REV.

i965: Add real support for texturing/rendering with MESA_FORMAT_RGBA8888_REV.

This was hacked in in one place for EGL image stuff, but the right
thing to do was just to provide the mapping from the mesa format to
the native hardware format, which includes render target support.

This turns out to be required for GL_ARB_texture_buffer_object, which
sees data in this layout.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>