sna: Guard use of DRM_MODE_OBJECT type ids

sna: Guard use of DRM_MODE_OBJECT type ids

These are not currently exported on OpenBSD and cause the build to fail.
Hide their use behind an ifdef guard for the time being.

"I noticed the following when trying to compile xf86-video-intel git on OpenBSD:

/usr/users/jsg/src/xf86-video-intel/src/sna/sna_display.c:2106: error: 'DRM_MODE_OBJECT_CRTC' undeclared (first use in this function)
/usr/users/jsg/src/xf86-video-intel/src/sna/sna_display.c:2106: error: (Each undeclared identifier is reported only once
/usr/users/jsg/src/xf86-video-intel/src/sna/sna_display.c:2106: error: for each function it appears in.)
/usr/users/jsg/src/xf86-video-intel/src/sna/sna_display.c:2107: error: 'DRM_MODE_OBJECT_PLANE' undeclared (first use in this function)"

Reported-by: Jonathan Gray
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>