wayland_egl: Fix drop shadows on radeon

wayland_egl: Fix drop shadows on radeon

Summary:
We're doing this all wrong.

We've asking for "at least 1 bit" of A, R, G, B color depth.

ARGB2101010 fits that nicely, so mesa on radeon gives it to us.

This only fixes the drop shadows though, it's entirely possible that
a fullscreen window without alpha would get ARGB2101010 instead of
XRGB8888, so this code probably needs a rethink for multiple engines.

Reviewers: devilhorns

Reviewed By: devilhorns

Subscribers: devilhorns, cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D7022