[nrf noup] boot: zephyr: Add NCS boot banner

Adds a boot banner which shows as MCUboot

Signed-off-by: Jamie McCrae <[email protected]>
(cherry picked from commit 8d31ad7)

Author: nordicjm

boot/zephyr/prj.conf

@@ -31,3 +31,6 @@ CONFIG_PICOLIBC=y
 ### Disable malloc arena because we don't need it
 CONFIG_COMMON_LIBC_MALLOC_ARENA_SIZE=0
 CONFIG_NRF_RTC_TIMER_USER_CHAN_COUNT=0
+
+# NCS boot banner
+CONFIG_NCS_APPLICATION_BOOT_BANNER_STRING="MCUboot"