msm: mdss: debugfs: xlog: refactor xlog dump

Make overall dump facility more reliable and more useable for
debugging: write xlog info to stdout; only un-logged and un-dumped
entries will be dumped out each dump; add func line number, pid and
time stamp difference for each entry; add index for each entry dump.
Format of the log is as follows:
name:line=>[entry:timestamp:delta][pid]:params
   Where:
   name: Name of the caller function
   line: Line in the source file
   entry: Index in the circular buffer
   timestamp: time when log was taken
   delta: time difference with previous log
   pid: process id
   params: parameters used to log information
      (these are specific to each log)

Change-Id: I32853ef7e27cc8ac34775ff492d60c801df61dba
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>