using add insetad of addi when Operand is more than 16 bits long

Change-Id: I7f9452381ed8b321ec71e68d0d90485508b69885
Reviewed-on: https://chromium-review.googlesource.com/c/1430619
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#59049}