usb: musb: am335x: add support for dual instance

AM335x and TI81xx platform has dual musb controller so updating the
musb_dspc.c to support the same.

Changes:
        - Moved otg_workaround timer to glue structure
        - Moved static local variable last_timer to glue structure
        - PHY on/off related cleanups

Signed-off-by: Ravi Babu <ravibabu@ti.com>
Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Signed-off-by: Santhapuri, Damodar <damodar.santhapuri@ti.com>
[afzal@ti.com: remove control module related modifications]
Signed-off-by: Afzal Mohammed <afzal@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>