egl: add dri2_setup_swap_interval helper

egl: add dri2_setup_swap_interval helper

The current two implementations - X11 and Wayland were identical,
barrind the upper limit.

Instead of having same code twice - introduce a helper and pass the
limit as an argument.

Thus as Android/DRM/others get support - they only need to call the
function ;-)

v2: Rebase on top of keeping ::swap_available

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com> (v1)