usb: phy: generic: allow multiples calls to usb_phy_generic_register()

it's now very easy to return a platform_device pointer
and have the caller pass it as argument when calling
usb_phy_generic_unregister().

Signed-off-by: Felipe Balbi <balbi@ti.com>

diff --cc drivers/usb/musb/am35x.c
Simple merge

diff --cc drivers/usb/musb/blackfin.c
Simple merge

diff --cc drivers/usb/musb/da8xx.c
Simple merge

diff --cc drivers/usb/musb/tusb6010.c
Simple merge

diff --cc drivers/usb/phy/phy-generic.c
Simple merge

diff --cc include/linux/usb/usb_phy_generic.h
Simple merge