drivers: net: cpsw: Enable Annexe F Time sync

Enable the Annex F Time Sync explicitly for DRA7x and AM4372.
With this enabled the L2 PTP is working.

while at that rename TS_BIT8 to TS_TTL_NONZERO

Signed-off-by: George Cherian <george.cherian@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>