drm/vmwgfx: Fix unlocked ioctl and add proper access control

This fixes up vmwgfx for the unlocked ioctl code to avoid
doing it in the driver. Also adds ioctl flags.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Jakob Bornecrantz <jakob@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>