[AMDGPU][MC] Clean up DPP bound_ctrl handling

At the moment, we set the BC bit in DPP for both bound_ctrl:0 and
bound_ctrl:1, for compatibility with sp3 (see PR35397). However, this
hack is only needed for GFX8. For newer GFXs, sp3 behaves as expected,
i.e. it sets the bit when bound_ctrl:1 and clears it when bound_ctrl:0.

This patch updates LLVM to do the same for GFX11 or newer. We preserve
the current behaviour for GFX9 and 10 so we don't break any existing
code.

Differential Revision: https://reviews.llvm.org/D149254