hwcontext_vulkan: remove duplicate code, port to use generic vulkan utils

The temporary AVFrame on staack enables us to use the common
dependency/dispatch code in prepare_frame().
The prepare_frame() function is used for both frame initialization
and frame import/export queue family transfer operations.
In the former case, no AVFrame exists yet, so, as this is purely
libavutil code, we create a temporary frame on stack. Otherwise,
we'd need to allocate multiple frames somewhere, one for each
possible command buffer dispatch.

libavutil/Makefile

@@ -195,7 +195,7 @@ OBJS-$(CONFIG_QSV)                      += hwcontext_qsv.o
 OBJS-$(CONFIG_VAAPI)                    += hwcontext_vaapi.o
 OBJS-$(CONFIG_VIDEOTOOLBOX)             += hwcontext_videotoolbox.o
 OBJS-$(CONFIG_VDPAU)                    += hwcontext_vdpau.o
-OBJS-$(CONFIG_VULKAN)                   += hwcontext_vulkan.o
+OBJS-$(CONFIG_VULKAN)                   += hwcontext_vulkan.o vulkan.o
 
 OBJS-$(!CONFIG_VULKAN)                  += hwcontext_stub.o
 

libavutil/vulkan.h

@@ -267,6 +267,19 @@ static inline int ff_vk_count_images(AVVkFrame *f)
     return cnt;
 }
 
+static inline const void *ff_vk_find_struct(const void *chain, VkStructureType stype)
+{
+    const VkBaseInStructure *in = chain;
+    while (in) {
+        if (in->sType == stype)
+            return in;
+
+        in = in->pNext;
+    }
+
+    return NULL;
+}
+
 /* Identity mapping - r = r, b = b, g = g, a = a */
 extern const VkComponentMapping ff_comp_identity_map;