soc: rw: Switch main clock on PM2 to LPOSC

On RW, normal configuration has all clock generators gated in PM2.
Only the LPOSC is available for main clock source since it is a low
power clock.

Many of the peripherals on the chip are still "on" and do need a
main clock source in order to be effective as wakeup sources
to the chip as intended. So we should make this switch for PM2
specifically in order to achieve desired wakeup capabilities.

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