sh: add pll_clk to sh7785

This patch converts the sh7785 pll implementation from the
all-in-one code in frqmr_recalc() and frqmr_build_rate_table()
to a separate struct clk. This allows us to remove the processor
specific multiplier and use generic rate table functions.

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