perf db-export: Add trace begin / end branch type variants

perf db-export: Add trace begin / end branch type variants

Add branch types to cover different combinations with "trace begin" or
"trace end".

Previously, the Intel PT decoder would indicate begin / end by a branch
from / to zero. That hides useful information, in particular when a
trace ends with a call. Before remedying that, prepare the database
export to export branch types with more combinations that include trace
begin / end.  In those cases extend the descriptions to include 'trace
begin' and 'trace end' separately.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20180920130048.31432-3-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>