perf machine: Introduce machine__kernel_maps()

perf machine: Introduce machine__kernel_maps()

That returns the a data structure contained the ordered list of kernel
modules + the main kernel maps, one more step in removing the
MAP__{FUNCTION,VARIABLE} split.

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-qsgbxfyaohc80c9ma049dubm@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>