Kconfig: Fix Kconfig for Intel ixgbe and igb PTP support.

Fix Kconfig file to make sure that PTP and IGB/IXGBE are both either
in-kernel or modules, not mixed.  Having the build status mixed causes
compile errors.

Signed-off-by: Carolyn Wyborny <carolyn.wyborny@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>