of_mdio: move of_mdio_parse_addr to header file

The of_mdio_parse_addr() helper function is useful to other code, but
the module dependency chain causes issues.  To work around this, we can
move of_mdio_parse_addr() to be an inline function in the header file.
This gets rid of the dependencies and still allows for the reuse of
code.

Reported-by: Liviu Dudau <liviu@dudau.co.uk>
Signed-off-by: Jon Mason <jon.mason@broadcom.com>
Fixes: 342fa196

 ("mdio: mux: make child bus walking more permissive and errors more verbose")
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>