arm64: dts: imx8m: assign clocks for A53

Assign IMX8M*_CLK_A53_SRC's parent to system pll1 and
assign IMX8M*_CLK_A53_CORE's parent to arm pll out as what
is done in drivers/clk/imx/clk-imx8m*.c, then we could remove
the settings in driver which triggers lockdep warning.

Reported-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Reviewed-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>