staging: drm/omap: add debugfs support

Right now just a tiler_map file to dump a 2d map of which areas in
tiler/dmm have pinned buffers (or reservations).  In the future more
could be added.

Signed-off-by: Rob Clark <rob@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>