sh: move sh clock-cpg.c contents to drivers/sh/clk-cpg.c

Move the CPG helpers to drivers/sh/clk-cpg.c V2.

This to allow SH-Mobile ARM to share the code with
SH. All functions except the legacy CPG stuff is moved.

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