drm: Disable sprites if they're broken
drm: Disable sprites if they're broken

Current sprite implementation has a color format bug.  Disable sprites
if they don't work and avoid spamming stderr and syslog.

Fantu/compositor-spice,krezovic/weston,sir-murray/weston,Fantu/compositor-spice,Gnurou/weston,eyolfson/weston,Tarnyko/weston-xdg_surface_present,Tarnyko/weston-xdg_surface_present,sir-murray/weston,xorgy/weston,krezovic/weston,giucam/weston,giucam/weston,mchalupa/weston,kwm81/weston,udoprog/weston,xorgy/weston,mchalupa/weston,jonnylamb/weston,kwm81/weston,jonnylamb/weston,Gnurou/weston,eyolfson/weston,udoprog/weston,Fantu/compositor-spice