linux5.11: move System.map to -dbg package.

Fedora makes it 600 in the main package, Debian has moved it to their
-dbg package. Since it can help break KASLR on arbitrary attacks and
isn't really useful most of the time, confine to -dbg package.

srcpkgs/linux5.11/template

@@ -325,5 +325,6 @@ linux5.11-dbg_package() {
 	short_desc+=" - debugging symbols"
 	pkg_install() {
 		vmove usr/lib/debug
+		vmove "boot/System.map-${_kernver}"
 	}
 }