ARM: i.MX27 clk: Separate DT and non-DT init procedure

This patch separates DT and non-DT clock initialization procedure,
so we can avoid a lot of unneeded clk_register_clkdev() for DT case.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>