Fixed a nasty layering violation in the edis source

code.  It used to #include the enhanced disassembly
information for the targets it supported straight
out of lib/Target/{X86,ARM,...} but now it uses a
new interface provided by MCDisassembler, and (so
far) implemented by X86 and ARM.

Also removed hacky #define-controlled initialization
of targets in edis.  If clients only want edis to
initialize a limited set of targets, they can set
--enable-targets on the configure command line.

llvm-svn: 101179