[AMDGPU] Assembler: change v_madmk operands to have same order as mad.

The constant is now at source operand 1 (previously at 2).
This is also how it is in legacy AMD sp3 assembler.
Update tests.

Differential Revision: http://reviews.llvm.org/D17984

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@263212 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed