drm: i915 updates

Add support for DRM_VBLANK_NEXTONMISS.
Bump minor for swap scheduling ioctl and secondary vblank support.
Avoid mis-counting vblank interrupts when they're only enabled for pipe A.
Only schedule vblank tasklet if there are scheduled swaps pending.

Signed-off-by: Dave Airlie <airlied@linux.ie>