Add kevent support to drm

[johalun0_gmail.com]

Summary

Wayland requires kevent for drm devices. This patch adds that to the 3.8 drm branch (current HEAD).

Question:
Should there be some testing to see if kevent is being used in the wake up function so we don't call mtx_lock() and knote() when we don't need to?

[wulf_cicgroup.ru]

sys/dev/drm2/drmP.h

422

struct drm_file has struct selinfo event_poll member already. Can it be used for kevents too?

423

Can dev->event_lock be reused to not introduce new mutex?
As I see, both notify and kqfilter functions run with this mtx taken

[johalun0_gmail.com]

I agree on both suggestions. Will test and see if works as expected.

[johalun0_gmail.com]

Not relevant anymore.