ip17xx: Consolidate operations with PHY registers

ip17xx: Consolidate operations with PHY registers

Call mdiobus_{read,write} instead of duplicating their code.

Introduce ip_phy_write_masked(), which changes a part of a register. Will
be used later in this patch series. Please note that it does not hold any
lock between reading and writing, so it is up to the caller to serialize.

Also add DUMP_MII_IO, which enables logging of all MII accesses.

Signed-off-by: Martin Mares <mj@ucw.cz>
Signed-off-by: Patrick Horn <patrick.horn@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@21709 3c298f89-4303-0410-b956-a3cf2f4a3e73