MLK-16442-2: clk: imx8qm: Add mux for DC clocks.

MLK-16442-2: clk: imx8qm: Add mux for DC clocks.

DC clocks can choose their clock source between PLL1, PLL2 and
bypass input.
This patch introduces a multiplexer in the dc clock topology to
allow this choice and introduces one set of parents that will be used
for both display0 and display1 clocks.

Clock paths tested:
    1. PLL2(dc0_pll1_clk)->DC0_DISP1(dc0_disp1_clk)->LVDS
    2. BYP(dc0_bypass0_clk)->DC0_DISP1(dc0_disp1_clk)->LVDS

(BuildInfo: SCFW 9e9f6ec6, IMX-MKIMAGE 0, ATF 0)

Signed-off-by: Adriana Reus <adriana.reus@nxp.com>
Reviewed by: Ranjani Vaidyanathan <Ranjani.vaidyanathan@nxp.com>