phy: improved lookup method

Separates registration of the phy and the lookup. The method
is copied from clkdev.c,

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

diff --cc Documentation/phy.txt
Simple merge

diff --cc drivers/phy/phy-core.c
Simple merge

diff --cc include/linux/phy/phy.h
Simple merge