common: usb: Update logic for usb.o, usb_hub.o and usb_storage.o

Now that we have consistently named symbols to enable USB host or gadget
controller support in SPL or full U-Boot, we do not need to
unconditionally build USB files nor depend on non-SPL symbols to know
when to build these common files.

Signed-off-by: Tom Rini <trini@konsulko.com>