clk-imx: clean up imx5_clocks_common_init

Spread it out like i.MX6 clocks code does so it's more readable.

Reorder by register and offset, especially CCGR.

Identify CPU_PODF move out, since this gets rid of the no-set-rate-parent
hack made to keep cpufreq-cpu0 working. Once we get gates into the DT
then the next step is move this first divider out there.

rename imx_clk_divider_fixedparent to imx_clk_divider_no_srp