Make paths relative to BR2_DEFCONFIG

Instead of hardcoding the magic '../N900_RescueOS/' path everywhere,
have buildroot pull package config files, patches, etc. from the
directory that holds the main defconfig file, wherever that may be.

buildrootconfig

@@ -11,9 +11,9 @@ BR2_TARGET_GENERIC_HOSTNAME="rescueos"
 BR2_TARGET_GENERIC_ISSUE="Welcome to RescueOS"
 BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_DEVTMPFS=y
 # BR2_TARGET_GENERIC_REMOUNT_ROOTFS_RW is not set
-BR2_ROOTFS_OVERLAY="../N900_RescueOS/fs-overlay"
-BR2_ROOTFS_POST_BUILD_SCRIPT="../N900_RescueOS/post-build.sh"
-BR2_PACKAGE_BUSYBOX_CONFIG="../N900_RescueOS/busyboxconfig"
+BR2_ROOTFS_OVERLAY="$(dir $(BR2_DEFCONFIG))fs-overlay"
+BR2_ROOTFS_POST_BUILD_SCRIPT="$(dir $(BR2_DEFCONFIG))post-build.sh"
+BR2_PACKAGE_BUSYBOX_CONFIG="$(dir $(BR2_DEFCONFIG))busyboxconfig"
 BR2_PACKAGE_BUSYBOX_SHOW_OTHERS=y
 BR2_PACKAGE_TAR=y
 BR2_PACKAGE_CRAMFS=y
@@ -39,7 +39,7 @@ BR2_TARGET_ROOTFS_CRAMFS=y
 BR2_LINUX_KERNEL=y
 BR2_LINUX_KERNEL_CUSTOM_TARBALL=y
 BR2_LINUX_KERNEL_CUSTOM_TARBALL_LOCATION="http://n900.quitesimple.org/rescueOS/sourcecode/kernel_source.tar.gz"
-BR2_LINUX_KERNEL_PATCH="../N900_RescueOS/kernel-patches/0001-net-wireless-wl1251-update-firmware-path.patch"
+BR2_LINUX_KERNEL_PATCH="$(dir $(BR2_DEFCONFIG))kernel-patches/0001-net-wireless-wl1251-update-firmware-path.patch"
 BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
-BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="../N900_RescueOS/kernel_config"
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="$(dir $(BR2_DEFCONFIG))kernel_config"
 BR2_LINUX_KERNEL_ZIMAGE=y