egl/dri2: Add display lock

egl/dri2: Add display lock

In preperation of relaxing eglapi to not hold a lock across driver
calls, but instead only for protecting it's own state, add our own
lock to protect code paths that need locking or have not been audited
yet.  The blocking calls (ClientWaitSyncKHR) or critical path and/or
blocking (MakeCurrent, SwapBuffers*) are lockless, as they have already
been audited for thread safety.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Acked-by: Eric Engestrom <eric@igalia.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18050>