MLK-16136-1 clk: imx: imx8mq: define DCSS root clocks.

MLK-16136-1 clk: imx: imx8mq: define DCSS root clocks.

Define three root clocks for DCSS module:

    .IMX8MQ_CLK_DISP_AXI_ROOT
    .IMX8MQ_CLK_DISP_APB_ROOT
    .IMX8MQ_CLK_DISP_RTRM_ROOT

These root clocks share one clock gate along with
'IMX8MQ_CLK_DISP_ROOT' clock. So change its type
to be shared gate clock too.

Signed-off-by: Fancy Fang <chen.fang@nxp.com>