The original bindings documentation was incomplete (missing pinctrl-names,
missing endpoint node properties) and the example was out of date.

Add the missing information and tidy up the text.
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Acked-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>