linux: add dma-buf and sync_file ioctl handlers

drm-kmod already implements the dma-buf and sync_file ioctls, but
linux_ioctl.c had no handler group for the 'b' and '>' magic bytes, so
the requests never reached it and returned EINVAL from
linux_ioctl_fallback(). Route the commands drm-kmod services to
sys_ioctl(), translating the direction bits with SETDIR(); everything
else still falls through to the fallback and keeps getting named in
dmesg.

Approved-by: adrian
Accepted-by: dumbbell
Signed-off-by: Nick Price <nprice@FreeBSD.org>
(cherry picked from commit d6a7e89504af337413af39fd121026f512c0a35d)