r8169: add support for RTL8125

This adds support for 2.5Gbps chip RTL8125, it's partially based on the
r8125 vendor driver. Tested with a Delock 89531 PCIe card against a
Netgear GS110MX Multi-Gig switch. Firmware isn't strictly needed,
but on some systems there may be compatibility issues w/o firmware.
Firmware has been submitted to linux-firmware.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/Kconfig

@@ -96,14 +96,19 @@ config 8139_OLD_RX_RESET
 	  old RX-reset behavior.  If unsure, say N.
 
 config R8169
-	tristate "Realtek 8169 gigabit ethernet support"
+	tristate "Realtek 8169/8168/8101/8125 ethernet support"
 	depends on PCI
 	select FW_LOADER
 	select CRC32
 	select PHYLIB
 	select REALTEK_PHY
 	---help---
-	  Say Y here if you have a Realtek 8169 PCI Gigabit Ethernet adapter.
+	  Say Y here if you have a Realtek Ethernet adapter belonging to
+	  the following families:
+	  RTL8169 Gigabit Ethernet
+	  RTL8168 Gigabit Ethernet
+	  RTL8101 Fast Ethernet
+	  RTL8125 2.5GBit Ethernet
 
 	  To compile this driver as a module, choose M here: the module
 	  will be called r8169.  This is recommended.