sh: sh7724 clock framework rewrite V3

This patch contains V3 of the sh7724 clock framework
rewrite. The new code makes use of the recently merged
div4, div6 and mstp32 helper code. Both extal and fll are
supported as input clocks to the pll. The div6 clocks are
fed through a divide-by-3 block.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>