amd: Move all amd/common code that depends on LLVM to amd/llvm.

amd: Move all amd/common code that depends on LLVM to amd/llvm.

This commit is a step towards the goal of being able to build RADV
without LLVM. In the future we would like to offer the option to
use RADV solely with ACO. There is still a need for the common AMD
code located in amd/common but the LLVM specific parts need to be
separated.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Acked-by: Marek Olšák <marek.olsak@amd.com>
Acked-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>