[POWERPC] mpc8272ads: defconfig

Default config file for mpc8272ads (powerpc port).Though relevant bits went
in, it is required to keep proper default configuration for the target,
which seems to be missed initially.

Signed-off-by: Vitaly Bordug <vbordug@ru.mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>