RFR: Use s-macro to keep GC phase enum and names in sync

[Zhengyu Gu]

To keep GC phase enum and phase names, parallel phase enum and timing 
data in sync, avoid bugs that caused by adding new enum values without 
adding responding names or worker data, etc.

Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/gc_phase_sync/webrev.00/

Test:

   tier2_gc_shenandoah (fastdebug and release)
   Eyeball gc+stats output


Thanks,

-Zhengyu