video: Allow a copy framebuffer with pre-allocated fb

At present it is not possible for the video driver to use a pre-allocated
frame buffer (such as is done with EFI) with the copy framebuffer. This
can be useful to speed up the display.

Adjust the implementation so that copy_size can be set to the required
size, with this being allocated if the normal framebuffer size is 0.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/video.h b/include/video.h
index 3f67a93..4d99e5d 100644
--- a/include/video.h
+++ b/include/video.h
@@ -24,6 +24,7 @@
  * @base: Base address of frame buffer, 0 if not yet known
  * @copy_base: Base address of a hardware copy of the frame buffer. See
  *	CONFIG_VIDEO_COPY.
+ * @copy_size: Size of copy framebuffer, used if @size is 0
  * @hide_logo: Hide the logo (used for testing)
  */
 struct video_uc_plat {
@@ -31,6 +32,7 @@
 	uint size;
 	ulong base;
 	ulong copy_base;
+	ulong copy_size;
 	bool hide_logo;
 };