target/i386: Use generic DISAS_* enumerators

This target is not sophisticated in its use of cleanups at the
end of the translation loop.  For the most part, any condition
that exits the TB is dealt with by emitting the exiting opcode
right then and there.  Therefore the only is_jmp indicator that
is needed is DISAS_NORETURN.

For two stack segment modifying cases, we have not yet exited
the TB (therefore DISAS_NORETURN feels wrong), but intend to exit.
The caller of gen_movl_seg_T0 currently checks for any non-zero
value, therefore DISAS_TOO_MANY seems acceptable for that usage.

Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
