clk: imx: scu: remove legacy scu clock binding support

clk: imx: scu: remove legacy scu clock binding support

Legacy scu clock binding are not maintained anymore, it has a very
limited clocks supported during initial upstreaming and obviously
unusable by products. So it's meaningless to keep it in
kernel which worse the code readability.
Remove it to keep code much cleaner.

Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>