powerpc/configs: Enable function trace by default

Most (all?) distros turn these on, so it makes sense to enable them
for testing coverage, and they're also useful for developers.

Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
[mpe: Reword change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>