[POWERPC] update {g5,iseries,pseries}_defconfigs

Updating the defconfigs for iseries, pseries, and G5.   Sticking with
the defaults, with the following exceptions:  I've turned off HW_RANDOM
for all three configs.   For G5, I've enabled SND_AOA and friends as
modules; this includes the FABRIC_LAYOUT, ONYX, TAS, TOONIE and
SOUNDBUS* config options.

Signed-off-by: Will Schmidt <will_schmidt@vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>