perf machine: Shorten machine__load_kallsyms() signature

perf machine: Shorten machine__load_kallsyms() signature

So far the only use is for MAP__FUNCTION, and since we're going to
remove that split, remove the map_type argument in machine__load_kallsyms().

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-5dhgh7x8g9hx5hpxlp3k08jp@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>