R600/SI: Rough first implementation of shouldClusterLoads

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217968 91177308-0d34-0410-b5e6-96231b3b80d8
R600/SI: Remove assert

Since read2 / write2 are emitted for 4-byte aligned 8-byte
accesses, these are seen by the scheduler.

The DAG scheduler is semi-deprecated, so just
ignore these for now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217969 91177308-0d34-0410-b5e6-96231b3b80d8