Moved Linux bcmrpi_defconfig into own file

configs/raspi_defconfig

@@ -15,7 +15,8 @@ BR2_LINUX_KERNEL=y
 BR2_LINUX_KERNEL_CUSTOM_GIT=y
 BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com/raspberrypi/linux.git"
 BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="423c680bd722670f4b39ea79089859df02b411b6"
-BR2_LINUX_KERNEL_DEFCONFIG="bcmrpi"
+BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="$(BR2_EXTERNAL)/board/raspi/linux.config"
 BR2_LINUX_KERNEL_ZIMAGE=y
 BR2_LINUX_KERNEL_DTS_SUPPORT=y
 BR2_LINUX_KERNEL_INTREE_DTS_NAME="bcm2708-rpi-b bcm2708-rpi-b-plus bcm2708-rpi-cm"