builddeb: Add automatic support for sparc64 architecture

We currently label 64-bit kernel packages as sparc (32-bit), mostly
because it was officially supported while sparc64 was not.  Now
neither is officially supported, so label these packages as sparc64.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/package/mkdebian

@@ -31,7 +31,7 @@ set_debarch() {
 	x86_64)
 		debarch=amd64 ;;
 	sparc*)
-		debarch=sparc ;;
+		debarch=sparc$(if_enabled_echo 64BIT 64) ;;
 	s390*)
 		debarch=s390x ;;
 	ppc*)