usb: musb: Fix a bug by making suspend interrupt available in device mode

As a part of aligning the ISR code for MUSB with the specs, the
ISR code was re-written. 

See Commit 1c25fda4 (usb: musb: handle 
irqs in the order dictated by programming guide)

With this the suspend interrupt came accidently under CONFIG_USB_MUSB_HDRC_HCD.

The fix brings suspend interrupt handling outside 
CONFIG_USB_MUSB_HDRC_HCD.

Signed-off-by: Maulik Mankad <x0082077@ti.com>
Cc: David Brownell <david-b@pacbell.net>
Acked-by: Felipe Balbi <felipe.balbi@nokia.com>
Cc: stable <stable@kernel.org> [.34]
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>