ARM: shmobile: add struct clk_ratio and fixed ratio clock macro

Renesas chip has many clocks inside,
and some of them are using fixed ratio via parent clock.
Current shmobile clock code is using own divX_recalc function
and divX_clk_ops.
This patch can reduce these code

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>