clk: imx8m: check mcore_booted before register clk

If mcore_booted is true, ignore the clk root gate registration and
this will simplify AMP clock management and avoid system hang unexpectly
especially Linux shutdown clk used by mcore.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
Link: https://lore.kernel.org/r/20220228124112.3974242-2-peng.fan@oss.nxp.com
[abelvesa@kernel.org: Removed if-case for when mcore_booted is true]
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>