USB: Debug: Add centralized debug buffer for USB drivers

Add a centralized debug buffer which can log events from all USB
drivers in gadget directory. This will help in debugging issue
from first instance rather than enabling dynamic debug log and
reproducing again.

Change-Id: Id0285d30bf640a63d904f1dd02dcd061f1819359
Signed-off-by: Tarun Gupta <tarung@codeaurora.org>
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>