Create shadow framebuffer

gpu.h

@@ -25,6 +25,7 @@ typedef struct {
 	VkImage depth_img;
 	VkDeviceMemory depth_mem;
 	VkImageView depth_view;
+	VkFramebuffer shadow_framebuf;
 	VkFramebuffer framebuffers[MAX_FRAMES_IN_FLIGHT];
 	VkShaderModule floor_vert_shader;
 	VkShaderModule model_vert_shader;