x86: fold Disp32S and Disp32

x86: fold Disp32S and Disp32

The only case where 64-bit code uses non-sign-extended (can also be
considered zero-extended) displacements is when an address size override
is in place for a memory operand (i.e. particularly excluding
displacements of direct branches, which - if at all - are controlled by
operand size, and then are still sign-extended, just from 16 bits).
Hence the distinction in templates is unnecessary, allowing code to be
simplified in a number of places. The only place where logic becomes
more complicated is when signed-ness of relocations is determined in
output_disp().

The other caveat is that Disp64 cannot be specified anymore in an insn
template at the same time as Disp32. Unlike for non-64-bit mode,
templates don't specify displacements for both possible addressing
modes; the necessary adjustment to the expected ones has already been
done in match_template() anyway (but of course the logic there needs
tweaking now). Hence the single template so far doing so is split.