drm: Create drm_send_event helpers

drm: Create drm_send_event helpers

Use them in the core vblank code and exynos/vmwgfx drivers.

Note that the difference between wake_up_all and _interruptible in
vmwgfx doesn't matter since the only waiter is the core code in
drm_fops.c. And that is interruptible.

v2: Adjust existing kerneldoc too.

Reviewed-by: Alex Deucher <[email protected]> (v1)
Acked-by: Daniel Stone <[email protected]>
Cc: Alex Deucher <[email protected]>
Cc: Thomas Hellstrom <[email protected]>
Cc: Inki Dae <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Laurent Pinchart <[email protected]>
[danvet: Squash in compile fixup, spotted by 0-day.]
Signed-off-by: Daniel Vetter <[email protected]>