intel/fs: Replace fs_visitor::bank_conflict_cycles() with stand-alone function.

This will be re-usable by the IR performance analysis pass.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/intel/compiler/brw_fs.h

@@ -167,7 +167,6 @@ public:
    bool opt_drop_redundant_mov_to_flags();
    bool opt_register_renaming();
    bool opt_bank_conflicts();
-   unsigned bank_conflict_cycles(const fs_inst *inst) const;
    bool register_coalesce();
    bool compute_to_mrf();
    bool eliminate_find_live_channel();