net: phy: Document core PHY structures

Add kerneldoc for the core PHY data structures, a few inline functions
and exported functions which are not already documented.

v2
Typos
g/phy/PHY/s

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/kapi.rst

@@ -134,6 +134,15 @@ PHY Support
 .. kernel-doc:: drivers/net/phy/phy.c
    :internal:
 
+.. kernel-doc:: drivers/net/phy/phy-core.c
+   :export:
+
+.. kernel-doc:: drivers/net/phy/phy-c45.c
+   :export:
+
+.. kernel-doc:: include/linux/phy.h
+   :internal:
+
 .. kernel-doc:: drivers/net/phy/phy_device.c
    :export: