kbuild/mkspec: support 'update-bootloader'-based systems

When uninstalling kernel RPM, we're unconditionally calling
"new-kernel-pkg --remove". This is useless on systems which are based on
'update-bootloader' script instead.

Support update-bootloader removal method as well in case the script is
present; contrary to new-kernel-pkg, this needs to be done in %postun,
otherwise update-bootloader will refuse to remove entry for kernel for
which the binary still exists.
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Michal Marek <mmarek@suse.com>

scripts/package/mkspec

@@ -143,6 +143,11 @@ echo "if [ -x /sbin/new-kernel-pkg ]; then"
 echo "new-kernel-pkg --remove $KERNELRELEASE --rminitrd --initrdfile=/boot/initramfs-$KERNELRELEASE.img"
 echo "fi"
 echo ""
+echo "%postun"
+echo "if [ -x /sbin/update-bootloader ]; then"
+echo "/sbin/update-bootloader --remove $KERNELRELEASE"
+echo "fi"
+echo ""
 echo "%files"
 echo '%defattr (-, root, root)'
 echo "/lib/modules/$KERNELRELEASE"