clk: imx: re-order and concentrate the same type of clk api

Re-order and concentrate the same type of clk api for better
code maintenance.

Cc: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>