vulkan: Device initialization

This initialized a Vulkan logical device according to compositor
preference, but does not yet do anything with it.

vulkan.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <sys/types.h>
+#include <vulkan/vulkan.h>
+
+struct vulkan {
+    VkInstance instance;
+    VkPhysicalDevice *devices;
+    uint32_t device_len;
+    VkPhysicalDevice physical_device;
+
+    VkDevice device;
+
+    struct {
+        PFN_vkGetMemoryFdKHR vkGetMemoryFdKHR;
+    } api;
+};
+
+void vulkan_destroy(struct vulkan *vk);
+struct vulkan *vulkan_create(dev_t preferred_device);