usb: ohci-da8xx: drop the vbus GPIO

All users now setup a fixed regulator for the vbus supply. We can drop
the vbus GPIO code.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>