scsi: ufs: debugfs: add option to read peer DME attribute

This patch adds the debugfs capability to read the DME attribute of
peer UniPro/M-PHY. This should help for debugging.

Change-Id: I26d3675bdda8b9fdf0f9aa6b81a1ffafbd828fd0
[subhashj@codeaurora.org: resolved trivial merge conflicts]
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
[venkatg@codeaurora.org: resolved trivial merge conflicts]
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>