compositor-drm: Retry atomic modeset if we get EBUSY
When hotplugging DP hubs with displays already connected quite often we get udev event and start setting the modes before the driver is really ready for the modeset.
This results in drmModeAtomicCommit failing with EBUSY.
Let's keep retying for 5s before giving up and messing up the environment for the user.
Signed-off-by: Arkadiusz Hiler firstname.lastname@example.org