scsi: ufs-qcom: add print suppressing debugfs mechanism

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

Change-Id: I2500b7621b631e260d98595ed8cfe7d5a496dc10
Signed-off-by: Dov Levenglick <dovl@codeaurora.org>
[cang@codeaurora.org: Resolved trivial merge conflicts]
Signed-off-by: Can Guo <cang@codeaurora.org>