gendwarfksyms: Expand base_type

gendwarfksyms: Expand base_type

Start making gendwarfksyms more useful by adding support for
expanding DW_TAG_base_type types and basic DWARF attributes.

Example:

  $ echo loops_per_jiffy | \
      scripts/gendwarfksyms/gendwarfksyms \
        --debug --dump-dies vmlinux.o
  ...
  gendwarfksyms: process_symbol: loops_per_jiffy
  variable base_type unsigned long byte_size(8) encoding(7)
  ...

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>