Add clock control support for sh7372 MSIOF hardware blocks.

No upstream sh7372 boards are making use of MSIOF0->2,
but the sh7372 hardware happens to come out of reset with
all MSIOF MSTP clocks _enabled_, so to save power we need
to implement a fix in software to shut down unused clocks.

This patch relies on the recently merged

 794d78fe

 drivers: sh: late disabling of clocks V2

to make sure the unused clocks get disabled as expected.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>