[test] Update llc checks for CodeGen/X86/avg.ll

The output of update_llc_test_checks.py on this test file has changed,
so the test file should be updated to minimize source changes in future
patches.

The test updates for this file appear to be limited to relaxations of
the form:

  -; SSE2-NEXT:    movq %rdi, -{{[0-9]+}}(%rsp) # 8-byte Spill
  +; SSE2-NEXT:    movq %rdi, {{[-0-9]+}}(%r{{[sb]}}p) # 8-byte Spill

This was suggested in https://reviews.llvm.org/D45995.

llvm-svn: 330758