phy: fix Kconfig dependencies

DM816x PHY uses usb_phy_* methods and because
of that, it must select USB_PHY, however, because
the drivers in question (DM816x, TWL4030 and
OMAP_USB2) sit outside of drivers/usb/ directory,
meaning they can be built even if USB_SUPPORT=n.

This patches fixes the dependencies by adding
USB_SUPPORT as a dependency and making all drivers
select USB_PHY (which cannot be selected through
menuconfig).

Note that this fixes some linking breakages when
building with randconfig.

Cc: Tony Lindgren <tony@atomide.com>
Cc: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>