configs/stm32f469_disco_xip: explicitly set the kernel version

The version of the kernel and its headers must be explicitly set because
if you keep the default setting, the kernel is continuously updated in
buildroot with the risk that its image + dtb grow so much that it again
exceeds the 2 MByte of the flash module.

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

configs/stm32f469_disco_xip_defconfig

@@ -1,9 +1,12 @@
 BR2_arm=y
 BR2_cortex_m4=y
+BR2_KERNEL_HEADERS_5_15=y
 # BR2_UCLIBC_INSTALL_UTILS is not set
 BR2_GCC_ENABLE_LTO=y
 BR2_ROOTFS_POST_BUILD_SCRIPT="board/stmicroelectronics/common/stm32f4xx/stm32-post-build.sh"
 BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="5.15.6"
 BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
 BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/stmicroelectronics/stm32f469-disco/linux-xip.config"
 BR2_LINUX_KERNEL_IMAGE_TARGET_CUSTOM=y