frontends/va: Allow drivers to allocate and use encode DPB surface buffers

Drivers can now allocate these buffers and use them directly.

(cherry picked from commit a4ef6eccb5c78c8080a944d8dd08f829902afc60)
See https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30843#note_2544865
for more details about discussion/cherry-picking.

Signed-off-by: David Rosca <david.rosca@amd.com>
Reviewed-By: Sil Vilerino <sivileri@microsoft.com>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30908>

src/gallium/include/pipe/p_video_codec.h

@@ -201,6 +201,13 @@ struct pipe_video_codec
                               struct pipe_picture_desc *picture,
                               void* bitstream_buf,
                               unsigned *size);
+
+   /**
+    * Creates a DPB buffer used for a single reconstructed picture.
+    */
+   struct pipe_video_buffer *(*create_dpb_buffer)(struct pipe_video_codec *codec,
+                                                  struct pipe_picture_desc *picture,
+                                                  const struct pipe_video_buffer *templat);
 };
 
 /**

src/gallium/include/pipe/p_video_state.h

@@ -719,6 +719,7 @@ struct pipe_h264_enc_dpb_entry
    uint32_t frame_idx;
    uint32_t pic_order_cnt;
    bool is_ltr;
+   struct pipe_video_buffer *buffer;
 };
 
 struct pipe_h264_enc_picture_desc
@@ -1106,6 +1107,7 @@ struct pipe_h265_enc_dpb_entry
    uint32_t id;
    uint32_t pic_order_cnt;
    bool is_ltr;
+   struct pipe_video_buffer *buffer;
 };
 
 struct pipe_h265_enc_picture_desc