AMDGPU: Define a schedule class for COPY.

COPY was lacking a scheduling class, define it to avoid regressions in
the upcoming change to the bidirectional MachineScheduler. Approved by
tstellar on IRC.

Differential Revision: http://reviews.llvm.org/D21540

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273751 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed