configs: stm32mp1: Enable OF_BOARD_FIXUP flag for stm32mp15_defconfig

Enable OF_BOARD_FIXUP for stm32mp15_defconfig.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Change-Id: I047f3a54107b2cf82dfe16cd5c413661189cd278
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/u-boot/+/382103
ACI: CITOOLS <MDG-smet-aci-reviews@list.st.com>
ACI: CIBUILD <MDG-smet-aci-builds@list.st.com>

Author: Patrice Chotard

configs/stm32mp15_defconfig

@@ -14,6 +14,7 @@ CONFIG_CMD_STM32PROG=y
 # CONFIG_ARMV7_NONSEC is not set
 CONFIG_SYS_LOAD_ADDR=0xc2000000
 CONFIG_FWU_NUM_IMAGES_PER_BANK=1
+CONFIG_OF_BOARD_FIXUP=y
 CONFIG_SYS_MEMTEST_START=0xc0000000
 CONFIG_SYS_MEMTEST_END=0xc4000000
 CONFIG_DISTRO_DEFAULTS=y