mvgbe: remove warning for unused methods

Some baords may use the GBE interface but they have no
phy connected to the interface and a direct MAC/MAC interface.
For them we need to get rid of compiler warnings.

Signed-off-by: Stefan Bigler <stefan.bigler@keymile.com>
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Acked-by: Prafulla Wadaskar <prafulla@marvell.com>

drivers/net/mvgbe.c

@@ -52,6 +52,7 @@ DECLARE_GLOBAL_DATA_PTR;
 #define MV_PHY_ADR_REQUEST 0xee
 #define MVGBE_SMI_REG (((struct mvgbe_registers *)MVGBE0_BASE)->smi)
 
+#if defined(CONFIG_MII) || defined(CONFIG_CMD_MII)
 /*
  * smi_reg_read - miiphy_read callback function.
  *
@@ -181,6 +182,7 @@ static int smi_reg_write(const char *devname, u8 phy_adr, u8 reg_ofs, u16 data)
 
 	return 0;
 }
+#endif
 
 /* Stop and checks all queues */
 static void stop_queue(u32 * qreg)