perf map: Use map->prot in place of type==MAP__FUNCTION

perf map: Use map->prot in place of type==MAP__FUNCTION

Equivalent, one step more in ditching enum map_type.

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-mrjjc87a4tpf896j5u4sql4e@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>