[sched-deps] Generalise usage of macro fusion to work on any two insns.
* sched-deps.c (try_group_insn): Generalise macro fusion hook usage
to any two insns. Update comment. Rename to sched_macro_fuse_insns.
(sched_analyze_insn): Update use of try_group_insn to
sched_macro_fuse_insns.
* config/i386/i386.c (ix86_macro_fusion_pair_p): Reject 2nd
arguments that are not conditional jumps.