usb: dwc: add support for super-speed function suspend

The USB 3.0 specification defines a new 'Function Suspend' feature.
This feature enables the USB host to put inactive composite device
functions in a suspended state even when the device itself is not
suspended.
This patch extends the existing framework of USB dwc driver
to properly support the 'Function Resume' and 'Function Remote Wakeup'
related features.

Change-Id: If7bbfa7d6a4ff70d4b44ede5fc258370b890df47
Signed-off-by: Danny Segal <dsegal@codeaurora.org>