scsi: ufs-debug: add debugfs capability to collect query statistics

This patch adds a new debugfs capability to collect query statistics.
It counts how many times each IDN (index) was sent to device for each
query opcode.

A usage example:
1. to clean current query statistics:
   echo 1 > /d/ufshcd0/stats/query_stats

2. to dump the current query statistics:
   cat /d/ufshcd0/stats/query_stats

This capability is always on, and can not be turned off.

Change-Id: I46ec405aae480c0dc161dca015b407bde6335cf7
Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>