perf c2c report: Add 'symbol' and 'dso' sort keys

They are to be displayed in the single cacheline output:

  symbol, dso

They are wrappers for global sort_sym and sort_dso sort entries with c2c
specific headers.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Joe Mario <jmario@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-6742e6g0r7n63y5wc4rrgxx5@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>