disp: msm: dp: skip creating dir when debugfs is disabled

When CONFIG_DEBUG_FS is disabled skip creating root directory.

Change-Id: I97bed925392b781b73687164ca55e6cb09f951fc
Signed-off-by: Rajat Gupta <rajatgu@codeaurora.org>
[rshaha@codeaurora.org: resolve trivial merge conflicts]
Signed-off-by: Rahul Shahare <rshaha@codeaurora.org>