[MIPS] QEMU: Add support for little endian mips

This very small patch adds support for little endian on the virtual QEMU
mips platform. The status of this platform is the same as the big endian
one, ie it is possible to boot a system with init=/bin/sh.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>