A few x86-64 disassembler cleanups.
* Define a bitfield reader for the rel32offs field in JMP/CALL
* Define FIND-CALLED-OBJECT which takes an interior pointer
to either an FDEFN or CODE and finds the object regardless
of what's in a code component's header.
Use it in MAYBE-NOTE-LISP-CALLEE to locate absolute jump targets.
* Fix 'displacement' printer to not accidentally print static funs
as both an assembler routine and #<FUNCTION foo>.
(because FIND-ASSEMBLER-ROUTINE will also find static functions)