Currently we parse through xf86Info.debug to check if we the modifiers
should be disabled. Handle that within DDX and pass GLAMOR_NO_MODIFIERS
into the glamor_init() flags.

This allows individual DDX control over the setting - say when modifiers
are woking OK with one implementation and not the other.

Most importantly, this removes the final xf86 piece from the codebase.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>