perf symbols: Split kernel symbol processing from dso__load_sym()

perf symbols: Split kernel symbol processing from dso__load_sym()

More should be done to split this function, removing stuff map
relocation steps from the actual symbol table loading.

Arch specific stuff also should go elsewhere, to tools/arch/ and
we should have it keyed by data from the perf_env either in the
perf.data header or from the running environment.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-236gyo6cx6iet90u3uc01cws@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>