[15] RFR (L): 8235824: C2: Merge AD instructions for AddReductionV and MulReductionV nodes

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/jbhateja/8235824/webrev.00/all/
https://bugs.openjdk.java.net/browse/JDK-8235824

Merge AD instructions for the following vector nodes:
   - AddReductionV*
   - MulReductionV*

Individual patches:
 
http://cr.openjdk.java.net/~vlivanov/jbhateja/8235824/webrev.00/individual

Testing: tier1-4, test run on different CPU flavors (KNL, CLX)

Contributed-by: Jatin Bhateja <jatin.bhateja at intel.com>
Reviewed-by: vlivanov, sviswanathan, jrose, ?

Best regards,
Vladimir Ivanov