MLK-20474 gpu: dcss: Switch back the dcss to the newly added SCCG pll clock

MLK-20474 gpu: dcss: Switch back the dcss to the newly added SCCG pll clock

Now that there is a generic SCCG clock added, it can also
be used by the DCSS. The HDMI_PHY_27M_CLK ref sel is hardcoded as parent
to VIDEO_PLL2 in dts.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Reviewed-by: Laurentiu Palcu <laurentiu.palcu@nxp.com>