We will be using the new parameter in an upcomig change. The TFU
unit has a limited list of supported formats, so for cases where
we don't want to do any pixel format conversions and we are just
copying raw image data, we want to be able to rewrite the underlying
image format to use a compatible format. We will be using this
in a follow-up patch that adds a TFU path for image copies. For this
purpose, we also, move the function definition up in the file
so it is available for that upcoming TFU path without having to
put its prototype earlier in the file.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <mesa/mesa!7809>