usb: xhci: Add support for secondary interrupters

Implement APIs to dynamically allocate and free secondary
event rings based upon interrupter number. Also add exported
APIs in usb core layer which allows secondary event ring
management via remote processor entity.

Change-Id: I5ee7d44d6cad8e35e22d3c1a027a1eec5d208585
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Mayank Rana <mrana@codeaurora.org>