start straightening out libedis's dependencies and make it fit

better in the llvm world.  Among other things, this changes:

1. The guts of libedis are now moved into lib/MC/MCDisassembler
2. llvm-mc now depends on lib/MC/MCDisassembler, not tools/edis,
   so edis and mc don't have to be built in series.
3. lib/MC/MCDisassembler no longer depends on the C api, the C
   API depends on it.
4. Various code cleanup changes. 

There is still a lot to be done to make edis fit with the llvm
design, but this is an incremental step in the right direction.

llvm-svn: 108869