soc: nxp: Do not change driver init priorities

Doesn't seem like there is any reason to be changing the
serial and ADC driver init priorities in the SOC defconfigs.
By default, clock control has priority 30, dma has priority 40,
and serial/adc have priority 50. This seems already to be the order
that is needed, and the original goal of these overrides, which
don't seem necessary anymore.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>