dma-buf: add reservation_object_lock_interruptible()

That's the only wrapper function missing and necessary to cleanup TTM.

Reviewed-and-Tested-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171109085909.1653-3-christian.koenig@amd.com