[POWERPC] Set efika's device_type to "soc"

Device type should be "soc" (as in lite5200.dts), compatible is
already set to "mpc5200".

Signed-off-by: Domen Puncer <domen.puncer@telargo.com>
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>