radv: implement VK_EXT_subgroup_size_control

radv: implement VK_EXT_subgroup_size_control

This extension allows to control the subgroup size by allowing a
varying subgroup size and also specifying a required subgroup size.

This implementation only allows to specify a required subgroup
size for compute shaders because there is some caveats with
other shader stages (eg. NGG with geometry shader). This
basically allows apps to use Wave32 for compute shaders.

This extension is enabled for all chips but only GFX10 supports
Wave32. ACO doesn't support it.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>