sh: sh7722 clock framework rewrite

This patch rewrites the sh7722 clock framework code.
The new code makes use of the recently merged div4,
div6 and mstp32 helper code. Both extal and dll are
supported as input clocks to the pll.

While at it, now when all SuperH Mobile processors
are converted, fix CONFIG_SH_CLK_CPG_LEGACY to depend
on CONFIG_ARCH_SHMOBILE.

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