zink: emit demote cap when using demote
VUID-VkShaderModuleCreateInfo-pCode-01377(ERROR / SPEC): msgNum: 1478567243 - Validation Error: [ VUID-VkShaderModuleCreateInfo-pCode-01377 ] Object 0: handle = 0x55f304e851c0, type = VK_OBJECT_TYPE_DEVICE; | MessageID = 0x5821254b | SPIR-V module not valid: Opcode DemoteToHelperInvocation requires one of these capabilities: DemoteToHelperInvocation
cc: mesa-stable