soc: arm: nxp_imx: use CMSIS SystemInit for all NXP iMX.RT SOCs

Use CMSIS SystemInit for all NXP iMX.RT SOCs, to simplify initialization
flow, and remove redundant code where possible.

Introduce Kconfigs to disable Cache at boot, since SystemInit will enable
code cache on these platforms, which may be undesirable behavior.

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