radv: Fix vkCmdCopyImage for 2d slices into 3d Images

radv: Fix vkCmdCopyImage for 2d slices into 3d Images

Previously the z offset of the destination image was being ignored. It
should be taken into account when copying into a 3d target.

Also, img_extent_el.depth was being incorrectly clamped to 1 due to the
source image being VK_IMAGE_TYPE_2D. This would result in the blit
failing to iterate over all the 3d slices. Instead we clamp to the
destination image type.

Fixes failures in CTS tests:
dEQP-VK.api.copy_and_blit.image_to_image.3d_images.*

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>