[LLVMGPU] Explicitly set configs for vector distribution pipeline lowering tests

[Groverkss]

This patch does two things:

• Before this patch, tests in pipeline_vector_distribute.mlir run select-lowering-config as well as the lowering pipeline together. This restricts us from testing lowering for different configs for the same kernel. This patch explicitly sets configuration for kernels in these tests. For configuration, we already have tests in config_vector_distribute.mlir which test kernel config logic for vector distribution.
• Tests for gfx940 and gfx1100 were in the same file. Since we set kernel configuration explicitly, running a test with a gfx1100 intrinsic with gfx940 test target chip would cause errors. This patch splits these tests into their own files.