tools: initial wrpc-dump, still bugged

The tool is meant to print internal data structures of the wrpc,
by running either on a dump file or a live system.

The code is an edited copy of wr-switch-sw/userspace/tools/wrs_dump_shmem.c,
so the data-dumping mechanism is from there.

bugs at this point:
   - all endianness stuff is bad (in wrs it was local, here we cross-dump)
   - data sizes are wrong (see next commit)
   - we miss checks for consistency
   - we can't open /dev/mem (for spec for example) or a elf file
   - docs are missing too
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>