clk: imx: Refactor entire sccg pll clk

Make the entire combination of plls to be one single clock. The parents used
for bypasses are specified each as an index in the parents list.
The determine_rate does a lookup throughout all the possible combinations
for all the divs and returns the best possible 'setup' which in turn is used
by set_rate later to set up all the divs and bypasses.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Tested-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>