soc: nxp: imxrt: Clean up INIT_SYS_PLL

Don't force select INIT_SYS_PLL at SOC level. Instead use default y so
that board can unset it. Keep previous case where we would default y
which was only on RT1040. Also, this config is not used in RT1170 soc,
so move it to RT10xx series kconfig instead of family level. And it
appears to be on all the RT10xx, so ifdef is not needed.

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