egl/wayland: use bitset.h for `formats` bit set

egl/wayland: use bitset.h for `formats` bit set

Currently only 7 formats are supported, but we don't want the 16 limit
(it's an `unsigned`) to hit us by surprise :]

Let's use bitset.h's BITSET magic to allow us to have any number of
formats, with a static assert to make sure we don't forget to update it.

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>