net: stmmac: Add hardware supported cross-timestamp

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>
diff --git a/drivers/net/ethernet/stmicro/stmmac/common.h b/drivers/net/ethernet/stmicro/stmmac/common.h
index 1c0c60b..9546905 100644
--- a/drivers/net/ethernet/stmicro/stmmac/common.h
+++ b/drivers/net/ethernet/stmicro/stmmac/common.h
@@ -388,6 +388,8 @@ struct dma_features {
 	unsigned int estsel;
 	unsigned int fpesel;
 	unsigned int tbssel;
+	/* Numbers of Auxiliary Snapshot Inputs */
+	unsigned int aux_snapshot_n;
 };
 
 /* RX Buffer size must be multiple of 4/8/16 bytes */