scsi: ufs: add print suppressing debugfs mechanism

Provides a mechanism for the userspace to suppress specific
debug prints via the debugfs. This is useful in order to avoid
cases where too much printing would cause watchdog timers to expire.

Change-Id: I1ab068cd616ddac767ec5f30ab130e3b1ac34e15
Signed-off-by: Dov Levenglick <dovl@codeaurora.org>
[imaund@codeaurora.org: Resolved context conflicts]
Signed-off-by: Ian Maund <imaund@codeaurora.org>
[subhashj@codeaurora.org: resolved trivial merge conflicts]
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
[cang@codeaurora.org: Resolved trivial merge conflicts]
Signed-off-by: Can Guo <cang@codeaurora.org>