perf callchain: Set callchain_param.enabled when parsing --call-graph

perf callchain: Set callchain_param.enabled when parsing --call-graph

Trying to move in the direction of using callchain_param for all
callchain parameters, eventually ditching them from symbol_conf.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-kixllia6r26mz45ng056zq7z@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>