scsi: ufs-debugfs: create statistics folder

In this patch a new folder is created under the debugfs/ufshcd<x>
root folder, in which all statistics information is located and collected.

Change-Id: I3ea68a7c75b8252b6ad8487ff927e0fe520242e4
Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>