usb: isp1760: Fix USB disabled check

The isp1760 driver registration function returns an error if USB is
disabled. This made sense when the driver only supported host
controllers, but now that it supports peripheral controllers host
support isn't mandatory anymore.

Fix this by returning an error only when both the HCD and UDC functions
are disabled, either through the kernel configuration or at runtime.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>