debian: Move to multi-arch support in libosmocore

Enable multi-arch support in libosmocore. This means the package
can not be built on squeeze anymore.

The concept of "foreign" is not really well documented but I
think I use it correctly here.
diff --git a/debian/libosmoctrl0.install b/debian/libosmoctrl0.install
index 6b23be8..56c64fc 100644
--- a/debian/libosmoctrl0.install
+++ b/debian/libosmoctrl0.install
@@ -1 +1 @@
-usr/lib/libosmoctrl*.so.*
+usr/lib/*/libosmoctrl*.so.*