stmmac: add the support for PTP hw clock driver

This patch implements PHC (ptp hardware clock) driver for stmmac
driver to support 1588 PTP.

V2: added support for FINE method, reduced loop delay and review spinlock.

Signed-off-by: Rayagond Kokatanur <rayagond@vayavyalabs.com>
Hacked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>