[llvm] [AMDGPU][True16][CodeGen] update GFX11Plus codegen test with true16 flag (PR #135078)

[Pierre van Houtryve via llvm-commits]

Pierre-vh wrote:

Why do all tests need to check this feature? Why not have a few dedicated test cases just to stress-test this?
I'm a bit uneasy seeing the amount of CHECK lines added in some tests (thousands, even 42k for one test). Our test suite can be pretty slow already so if we're going to add this many check lines it has to be worth it, IMO.

https://github.com/llvm/llvm-project/pull/135078