boards: mimxrt11xx: Enable Flash driver on RT1160 and RT1170

Enable the flash on RT1170 and RT1160. When booting from the CM7 core,
flash will be started in XIP mode and used as storage as well as boot
memory. When booting from the CM4 core, flash is available as storage
only, and does not run in XIP mode.

This commit was tested with the following samples
-flash_shell
-littlefs

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