net: phy: Move linkmode helpers to somewhere public

phylink has some useful helpers to working with linkmode bitmaps.
Move them to there own header so other code can use them.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/mii.h

@@ -10,6 +10,7 @@
 
 
 #include <linux/if.h>
+#include <linux/linkmode.h>
 #include <uapi/linux/mii.h>
 
 struct ethtool_cmd;