drm/msm: limit sde_dbg_dump output to current entries

Update the sde_dbg_dump function to only dump event log
entries up to the time the dump is initiated, and increase
the number of recorded event log entries.

This places a limit on the total number of entries that are
output to the dmesg log even if more entries would have been
added while the dump is executing (e.g., interrupt events),
while still allowing the extra events to be recorded properly.

Change-Id: I66f850d21a2d0217f9049facffce074831b7e17d
Signed-off-by: Clarence Ip <cip@codeaurora.org>