radv: implement AMD_shader_ballot extension
This series implements the following Vulkan extensions via the existing Vulkan 1.1 subgroup functionality:
- VK_EXT_shader_subgroup_vote
- VK_EXT_shader_subgroup_ballot
Additionally, for RADV, it implements
- VK_AMD_shader_ballot
Due to the strong performance hit in games like DOOM (2016), the extension is disabled by default, and can be enabled by adding RADV_PERFTEST=ballot to the command line.