ARM: shmobile: r7s72100: document MSTP clock support

ARM: shmobile: r7s72100: document MSTP clock support

Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
(cherry picked from commit b557deadc5cca47aff93781b21fef468233c2ea8)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Conflicts:
	Documentation/devicetree/bindings/clock/renesas,cpg-mstp-clocks.txt