dt-bindings: clean up rockchip grf binding document

Fixup some typos and inconsistencies in the grf binding.

Signed-off-by: Peter Geis <pgwipeout@gmail.com>
Link: https://lore.kernel.org/r/20191028182254.30739-3-pgwipeout@gmail.com


Signed-off-by: Heiko Stuebner <heiko@sntech.de>