egl/wayland: Use an array for modifiers

egl/wayland: Use an array for modifiers

Each Wayland EGLDisplay currently contains a struct with one vector of
modifiers per format, hardcoded in the header. To allow easier support
for more formats, turn this into an array of u_vectors which is opaque
outside of platform_wayland.c.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Tested-by: Ilia Mirkin <imirkin@alum.mit.edu>