scsi: ufs: add debug counters for recoverable errors during runtime

There is no way to know how many times various UFS errors happened
while system is running if we have successfully recovered from those
errors. Those failures should be counted and inspected as they might be
anomaly behavior of the driver and can impact performance.
This change adds support to capture these failures statistics like how
many times we have seen errors, and which type of errors.

To reset the counters:
echo 1 > /sys/kernel/debug/ufs/err_stats

To print them out:
cat /sys/kernel/debug/ufs/err_stats

Note: There is no need to enable them as they are never disabled.
This error counters are something that we always would like to have.

Change-Id: I559c729b998f79c6bdda2da54c0f0ec7531696d7
Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>