AMDGPU/GlobalISel: Add support for llvm.amdgcn.kernarg.segment.ptr

Note a normal select test is not currently possible because this
relies on input registers tracked in SIMachineFunctionInfo which
are not currently serializable in MIR, but this does work end-to-end
from the IR.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@335490 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed