drm/amd/display: Make DMCUB tracebuffer debugfs chronological

[Why]

Previously, the debugfs did a simple dump of the tracebuffer region.
Because the tracebuffer is a ring, it meant that the entries printed may
not be in chronological order if the ring rolled over. This makes
parsing the tracelog cumbersome.

[How]

Since dmcub provides the current entry count, use that to determine
the latest tracelog entry and output the log chronologically.

Also, the fb region size is not accurate of the actual tracebuffer size;
it has been padded to alignment requirements. Use the tracebuffer size
reported by the fw meta_info, if available. If not, a fallback to the
hardcoded default is needed. To make this value available to other .c
files, its define was moved to dmub_srv.h.

Also, print a indicator at the start of the log if rollover occurred.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>