RAUC: turn this into a configurable target

I am not using the generic rootfs target because it is optimized for
using fakeroot, and because it extracts that tarball from rootfs-common.
Rather than fighting the hooks (ROOTFS_XXX_POST_GEN_HOOKS is the only
thing which runs outside of fakeroot) and doing extra work by unpacking,
let's go all the way down to raw Makefile.

Change-Id: I075204291fbeac8d1af97a0a7c1254054ef1f594
diff --git a/package/Config.in b/package/Config.in
index 64d8537..17cd498 100644
--- a/package/Config.in
+++ b/package/Config.in
@@ -1,4 +1,5 @@
 source "$BR2_EXTERNAL_CZECHLIGHT_PATH/package/cla-sysrepo/Config.in"
 source "$BR2_EXTERNAL_CZECHLIGHT_PATH/package/czechlight-cfg-fs/Config.in"
+source "$BR2_EXTERNAL_CZECHLIGHT_PATH/package/czechlight-rauc/Config.in"
 source "$BR2_EXTERNAL_CZECHLIGHT_PATH/package/czechlight-separate-boot/Config.in"
 source "$BR2_EXTERNAL_CZECHLIGHT_PATH/package/grub2-tools/Config.in"