[NFC][AMDGPU] Add tests for dependent v_bfi instructions.

This commit adds a few tests which are used to test the codegen
of nested v_bfi instructions. These instruction sequences are
being generated when using the canonical form for bitfieldInsert
and having the sequences being transformed by SimplifyDemandedBits.

This is a pre-commit for a change which enables the backend to
lower these instruction sequences into v_bfi instructions.