clk: imx8mn: A53 core clock no need to be critical

'A53_CORE' is just a mux and no need to be critical, being critical
will cause its parent clock always ON which does NOT make sense,
to make sure CPU's hardware clock source NOT being disabled during
clock tree setup, need to move the 'A53_SRC'/'A53_CORE' reparent
operations to after critical clock 'ARM_CLK' setup finished.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>