net: stmmac: Add hardware supported cross-timestamp

commit 341f67e4

 upstream.

Cross timestamping is supported on Integrated Ethernet Controller in
Intel SoC such as EHL and TGL with Always Running Timer.

The hardware cross-timestamp result is made available to
applications through the PTP_SYS_OFFSET_PRECISE ioctl which calls
stmmac_getcrosststamp().

Device time is stored in the MAC Auxiliary register. The 64-bit System
time (ART timestamp) is stored in registers that are only addressable
by using MDIO space.

Signed-off-by: Tan Tee Min <tee.min.tan@intel.com>
Co-developed-by: Wong Vee Khee <vee.khee.wong@linux.intel.com>
Signed-off-by: Wong Vee Khee <vee.khee.wong@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Yongxin Liu <yongxin.liu@windriver.com>