MIPS: Enable vmlinuz for JZ4740

This patch adds support for building a compressed kernel for the JZ4740
architecture.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
Cc: Sergei Shtylyov <sshtylyov@mvista.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3563/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>