sh: sh7366 mstp32 index rework

This patch adds sh7366 MSTP enums for mstp_clks[] index.
The MSTP bit for the SIU is removed as well since it is
not included in the documentation. Most likely an old
copy paste error from sh7722.

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