soc: rt10xx: Add power management support

Add power management code for the RT10xx SOC. By default, the code will
simply gate the core clock and transition the SOC to WAIT mode when
sleeping, but if clocking hooks are register to reduce clock frequencies
these will be called as well, and the SOC core voltage will be lowered
for additional power savings.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>