AMDGPU/GFX10: implement ds_ordered_count changes

Summary:
ds_ordered_count can now simultaneously operate on up to 4 dwords
in a single instruction, which are taken from (and returned to)
lanes 0..3 of a single VGPR.

Change-Id: I19b6e7b0732b617c10a779a7f9c0303eec7dd276

Reviewers: mareko, arsenm, rampitec

Subscribers: kzhuravl, jvesely, wdng, yaxunl, dstuttard, tpr, t-tye, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63716

llvm-svn: 364815