sh: clkfwk: add sh_clk_fsidiv_register()

This patch adds sh_clk_fsidiv_register() to share FSI-DIV clock code

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Simon Horman <horms@verge.net.au>