boards/arm: nucleo_f207zg: Enabling flash support in device tree.
boards/arm: nucleo_f207zg: Enabling flash support in device tree.

This commit enables flash support for nucleo-f207zg in device tree.
The last sector of 128KB is used as storage partition.

Signed-off-by: Krishna Mohan Dani <2f92acbcef6b57b10df043e51f4a57d8454f58b9@hcl.com>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr