qemu/mipsel-malta: update readme and use kernel version 3.2

Update configuration to use kernel version 3.2
Also update the readme to use buildroot basedir as a reference for
kernel and rootfs like the other samples do.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>