usb: Makefile: fix drivers/usb/phy/ Makefile entry

drivers/usb/phy/ should be compiled everytime
we have CONFIG_USB_OTG_UTILS enabled.

phy/ should've been part of the build process based
on CONFIG_USB_OTG_UTILS, don't know where I had my head
when I allowed CONFIG_USB_COMMON there.

In fact commit c6156328
tried to fix a previous issue but it made things even
worse.

The real solution is to compile phy/ based on
CONFIG_USB_OTG_UTILS which gets selected by all PHY
drivers.

I only triggered the error recently after accepting a
patch which moved a bunch of code from otg/otg.c to
phy/phy.c and running 100 randconfig cycles.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>