configs/broadcom_northstar_defconfig: specify kernel & headers versions

Even though Northstart platform support is well upstreamed it may always
happen that some kernel change affects/breaks something. It's a good
practice to specify fixed versions for kernel & Linux headers.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

configs/broadcom_northstar_defconfig

@@ -1,7 +1,10 @@
 BR2_arm=y
 BR2_cortex_a9=y
+BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_6_6=y
 BR2_ROOTFS_POST_IMAGE_SCRIPT="board/broadcom/northstar/post-image.sh"
 BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="6.6.9"
 BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
 BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/broadcom/northstar/linux.config"
 BR2_LINUX_KERNEL_APPENDED_ZIMAGE=y