drm/gem: move drm_gem_object_handle_unreference_unlocked into drm_gem.c

drm/gem: move drm_gem_object_handle_unreference_unlocked into drm_gem.c

We have three callers of this function now and it's neither
performance critical nor really small. So an inline function feels
like overkill and unecessarily separates the different parts of the
code.

Since all callers of drm_gem_object_handle_free are now in drm_gem.c
we can make that static (and remove the unused EXPORT_SYMBOL). To
avoid a forward declaration move it (and drm_gem_object_free_bug) up a
bit.

Change-Id: I383dd0f8a20c28e587fda7f511bb43aabae03cd2
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>