usb: musb: add musb_ida for multi instance support

Added musb_ida in musb_core.c to manage the multi core ids.

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>
Signed-off-by: Felipe Balbi <balbi@ti.com>