Fix sigFPE in HIP blocksize deduction

[skyreflectedinmirrors]

Requires #3333 for testing on ROCm 3.7

The:

  using Policy =
      Kokkos::TeamPolicy<ExecutionSpace, Kokkos::LaunchBounds<32, 1>>;

in test_block_deduction_bug_pr_3103, causes:

int block_size = std::min(attr.maxThreadsPerBlock, max_threads_per_block);

to be set to 32 (as this takes the 3.7 path). This forces:

(block_size / HIPTraits::WarpSize))

to zero, resulting in a sigFPE.

I've also added a guard on regs_per_wavefront in case we ever launch a null kernel, and attr.numRegs is somehow zero.

[masterleinad]

Looks OK to me. We should see if this helps in #3333.

[skyreflectedinmirrors]

All the HIP tests in 3.5 are passing, CUDA is failing with no devices present -- probably just needs a re-test?

[dalg24]

Retest this please