soc: nxp_imx: Fix enabling ENET PLL outputs

The ENET PLL should be enabled if the SoC is the MIMXRT1021 (it used by
the ARM core) or if the ENET device is enabled.

The 500MHz clock should be enabled if the SoC is the MIMXRT1021.

The ENET clock should be enabled if the ENET device is enabled.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>