Merging r262732:

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r262732 | thomas.stellard | 2016-03-04 10:31:18 -0800 (Fri, 04 Mar 2016) | 12 lines

AMDGPU/SI: Add support for spiling SGPRs to scratch buffer

Summary:
This is necessary for when we run out of VGPRs and can no
longer use v_{read,write}_lane for spilling SGPRs.

Reviewers: arsenm

Subscribers: arsenm, llvm-commits

Differential Revision: http://reviews.llvm.org/D17592

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llvm-svn: 271722