powerpc/configs: Add CONFIG_RAS now required for CONFIG_EDAC

In commit e3c4ff6d ("EDAC: Remove EDAC_MM_EDAC") CONFIG_EDAC grew
a dependency on CONFIG_RAS. Some of our defconfigs don't have the
latter, which means we lose CONFIG_EDAC, so add CONFIG_RAS to fix
that.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>