net: macb: Remove obsolete comment from Kconfig

The Kconfig file says that Gigabit mode is not supported, but it has been
supported since commit 140b7552 ("net/macb:
Add support for Gigabit Ethernet mode").
Signed-off-by: NJames Byrne <james.byrne@origamienergy.com>
Acked-by: NNicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/Kconfig

@@ -35,8 +35,8 @@ config MACB
 	---help---
 	  The Cadence MACB ethernet interface is found on many Atmel AT32 and
 	  AT91 parts.  This driver also supports the Cadence GEM (Gigabit
-	  Ethernet MAC found in some ARM SoC devices).  Note: the Gigabit mode
-	  is not yet supported.  Say Y to include support for the MACB/GEM chip.
+	  Ethernet MAC found in some ARM SoC devices).  Say Y to include
+	  support for the MACB/GEM chip.
 
 	  To compile this driver as a module, choose M here: the module
 	  will be called macb.