soc: nxp: imxrt: imxrt118x: add flexspi support

add flexspi.c file to get flexspi clock rate.

Enable flexspi1 clock if don't boot from flash.

Use custom fixed mpu_regions.c file to config MPU for CM7

Signed-off-by: Lucien Zhao <lucien.zhao@nxp.com>
6 files changed