tg3 / broadcom: Add PHY_BRCM_CLEAR_RGMII_MODE flag

Broadcom 50610M parts changed the default definitions of the RGMII mode
shadow register.  The 5785 needs the RGMII mode selection bits [4:3]
cleared.

The default value of the remaining bits in this register are zero.
Rather than unnecessarily burn an extra bit in the dev_flags member in
an attempt to enumerate all possible combinations, this patch take a
more course grained approach and labels the option as "clear all bits".

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/brcmphy.h b/include/linux/brcmphy.h
index daa1480..6e7ffce 100644
--- a/include/linux/brcmphy.h
+++ b/include/linux/brcmphy.h
@@ -8,4 +8,5 @@
 #define PHY_BRCM_STD_IBND_DISABLE	0x00000800
 #define PHY_BRCM_EXT_IBND_RX_ENABLE	0x00001000
 #define PHY_BRCM_EXT_IBND_TX_ENABLE	0x00002000
+#define PHY_BRCM_CLEAR_RGMII_MODE	0x00004000
 #define PHY_BCM_FLAGS_VALID		0x80000000