Remove all the backend code to support drivers without universal planes.
From[1]:
"The code needed to support kernels where DRM does not support uiniversal
planes makes the DRM-backend a little more complicated, because it needs
to create fake planes for primary and cursor. The lifetimes of the fake
planes does not match the lifetime of "proper" planes, which is surprising."
And since the universal planes left the experimetal flag in 2014[2] it is
safe to remove the support now.
[1] https://gitlab.freedesktop.org/wayland/weston/-/issues/427
[2] https://cgit.freedesktop.org/drm/drm-tip/commit/?id=c7dbc6c9ae5c3baa3be755a228a349374d043b5b
Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@gmail.com>