usb: musb: musb_host: Enable HCD_BH flag to handle urb return in bottom half

Enable HCD_BH flag for musb host controller driver.
This improves the MSC/UVC through put. With this enabled
even 640x480@30fps webcam streaming is also supported.

Signed-off-by: George Cherian <george.cherian@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>