usb: common: rework CONFIG_USB_COMMON logic

The phy-am335x driver selects 'USB_COMMON', but all other drivers
use 'depends on' for that symbol, and it depends on USB || USB_GADGET
itself, which causes a Kconfig warning:

warning: (AM335X_PHY_USB) selects USB_COMMON which has unmet direct dependencies (USB_SUPPORT && (USB || USB_GADGET))

As suggested by Felipe Balbi, this turns the logic around, and makes
'USB_COMMON' selected by everything else that needs it, so we can
remove the dependencies.

Fixes: 59f042f6 ("usb: phy: phy-am335x: bypass first VBUS sensing for host-only mode")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Felipe Balbi <balbi@kernel.org>
Reviewed-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>