boards: arm: Add mcuboot and flash storage partitions to mimxrt1060_evk

Adds flash partitions and chosen nodes to the mimxrt1060_evk device tree
to support mcuboot and storage on the external QSPI flash. This flash is
rated for 100K minimum program-erase cycles per sector, therefore this
partition configuration supports approximately 100K / (3072/128) = 4167
upgrades.

Also enables FlexSPI flash driver XIP mode support on this board to
support mcuboot.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>