AMDGPU: Explicitly define a triple for some tests

Summary:
This is related to the changes to the groupstaticsize intrinsic in
D61494 which would otherwise make the related tests in these files
fail or much less useful.

Note that for some reason, SOPK generation is less effective in the
amdhsa OS, which is why I chose PAL. I haven't investigated this
deeper.

Change-Id: I6bb99569338f7a433c28b4c9eb1e3e036b00d166

Reviewers: arsenm

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63392

llvm-svn: 363600