msm: mdss: debugfs: xlog: add debug xlog

When MDSS_XLOG_DBG entries are inserted into code, these entries are
always logged regardless enable status. This helps use xlog in quick
debugging and none of these entries should be merged.

Change-Id: Iebcf6cb7fc32bc77281e2f02a354f35357ff6d88
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>