drm: Use of-graph helpers to loop over endpoints

Convert all drm callers that use of_graph_get_next_endpoint to loop over
of-graph endpoints to the newly introduced for_each_endpoint_of_node
helper macro.

* tag 'of-graph-drm-2015-04-08' of git://git.pengutronix.de/git/pza/linux:
  drm/rockchip: use for_each_endpoint_of_node macro, drop endpoint reference on break
  drm/rcar-du: use for_each_endpoint_of_node macro
  drm/imx: use for_each_endpoint_of_node macro in imx_drm_encoder_get_mux_id
  drm: use for_each_endpoint_of_node macro in drm_of_find_possible_crtcs
  of: Explicitly include linux/types.h in of_graph.h
  dt-bindings: brcm: rationalize Broadcom documentation naming
  of/unittest: replace 'selftest' with 'unittest'
  Documentation: rename of_selftest.txt to of_unittest.txt
  Documentation: update the of_selftest.txt
  dt: OF_UNITTEST make dependency broken
  MAINTAINERS: Pantelis Antoniou device tree overlay maintainer
  of: Add of_graph_get_port_by_id function
  of: Add for_each_endpoint_of_node helper macro
  of: Decrement refcount of previous endpoint in of_graph_get_next_endpoint