Machine file names should not have prefix "mips_".

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
Message-id: <20200518200920.17344-22-aleksandar.qemu.devel@gmail.com>
[PMD: Fixed Fuloong line conflict due to rebase]
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>