rpm: do not build empty debuginfo package

The kernel is compiled without debug symbols, so kernel-debuginfo
package was useless. If one want debuginfo package, he/she need to
reenable it *and* compile kernel with debug symbols (which need a lot of
disk space).

kernel.spec

@@ -33,6 +33,10 @@
 
 %define install_vdso 1
 
+# If you want to build debuginfo package, enable also CONFIG_DEBUG_INFO in %%setup section
+# Otherwise debuginfo build is disabled by default to save disk space (it needs 2-3GB build time)
+%global debug_package %{nil}
+
 Name:           kernel
 Summary:        The Xen Kernel
 Version:        %{version}