ptp: fixup Kconfig for two PHC drivers.

Ben Hutchings recently came up with a better way to handle the kconfig
dependencies for the PTP hardware clocks. This patch converts one new and
one older driver to the new scheme.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>