egl/drm: Use modifiers for backbuffer creation
egl/drm: Use modifiers for backbuffer creation

Split into a separate patch from the previous patch as requested by
Emil.

Requested-by: Emil Velikov <f20878473f414da183da19ee25c8722cc1d711e4@collabora.com>
Signed-off-by: Ben Widawsky <73675debcd8a436be48ec22211dcf44fe0df0a64@bwidawsk.net>
Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler