configs/qemu_mips64_malta: update config

Slim down the kernel config, switch to ext4 (with ext2/3 support),
enable N32 & O32 ABI compatibility for extra testing goodness and enable
keyboard & mouse support.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>