Restructure and add a defconfig for BeagleBone Black

...which builds upon work by Pieter Smith that was imported in the
previous commit.

Change-Id: I9e83096c45cd83b0bc4e687a64075369b70d0661
diff --git a/configs/czechlight_i686_container_defconfig b/configs/czechlight_i686_container_defconfig
index e78ee79..4f9ed35 100644
--- a/configs/czechlight_i686_container_defconfig
+++ b/configs/czechlight_i686_container_defconfig
@@ -29,4 +29,4 @@
 # BR2_PACKAGE_VIM_RUNTIME is not set
 BR2_TARGET_ROOTFS_TAR_XZ=y
 CZECHLIGHT_NETCONF=y
-BR2_ROOTFS_OVERLAY="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight_i686_container/overlay/"
+BR2_ROOTFS_OVERLAY="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/i686_container/overlay/"