kbuild: deb-pkg: add debarch for ARCH=um

'make ARCH=um bindeb-pkg' shows the following warning.

  $ make ARCH=um bindeb-pkg
     [snip]
    GEN     debian

  ** ** **  WARNING  ** ** **

  Your architecture doesn't have its equivalent
  Debian userspace architecture defined!
  Falling back to the current host architecture (amd64).
  Please add support for um to ./scripts/package/mkdebian ...

This commit hard-codes i386/amd64 because UML is only supported for x86.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

Author: masahir0y

scripts/package/mkdebian

@@ -70,6 +70,13 @@ set_debarch() {
 			debarch=sh4$(if_enabled_echo CONFIG_CPU_BIG_ENDIAN eb)
 		fi
 		;;
+	um)
+		if is_enabled CONFIG_64BIT; then
+			debarch=amd64
+		else
+			debarch=i386
+		fi
+		;;
 	esac
 	if [ -z "$debarch" ]; then
 		debarch=$(dpkg-architecture -qDEB_HOST_ARCH)