Deb: Build RocksDB only on 64-bit and small endian architectures

RocksDB configure step checks that platform is 64-bit and little endian,
so limit the .deb packages to be built only on those platforms.

List of official Debian platforms at
https://www.debian.org/ports/index.en.html

debian/control

@@ -534,7 +534,7 @@ Description: Connect storage engine for MariaDB
  This package contains the Connect plugin for MariaDB.
 
 Package: mariadb-plugin-rocksdb
-Architecture: any
+Architecture: amd64 arm64 mips64el ppc64el
 Depends: mariadb-server-10.3 (= ${binary:Version}),
          ${misc:Depends},
          ${shlibs:Depends}