usb: musb: drop dangling CONFIG_USB_MUSB_DEBUG

CONFIG_USB_MUSB_DEBUG option was removed in

5c8a86e1 usb: musb: drop unneeded musb_debug trickery

to cleanup the code from driver specific debug facilities.  This patch
drops the last references to the musb debug config option,
unconditionally enabling all debug code paths, thus letting that code
being dropped at compile time if not needed.

Signed-off-by: Fabio Baltieri <fabio.baltieri@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>