powerpc: Enable CONFIG_SATA_AHCI on pseries and ppc64 defconfigs

We are starting to see ppc64 boxes with SATA AHCI adapters in it,
so enable it in our defconfigs.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>