Create shadow map image

gpu.h

@@ -19,6 +19,9 @@ typedef struct {
 	VkExtent2D swapchain_extent;
 	uint32_t swapchain_img_count;
 	VkImageView swapchain_img_views[MAX_FRAMES_IN_FLIGHT];
+	VkImage shadow_img;
+	VkDeviceMemory shadow_mem;
+	VkImageView shadow_view;
 	VkImage depth_img;
 	VkDeviceMemory depth_mem;
 	VkImageView depth_view;