usb: musb: add musb_host_setup() and musb_host_cleanup()

This patch re-introduces the bits that are necessary to use the musb
controller in host mode.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Felipe Balbi <balbi@ti.com>