staging: ion: remove struct page_info

ION system heap creates a temporary list of pages to build
scatter/gather table, introducing an internal data type, page_info. Now
that the order field has been removed from it, we do not need to depend
on such data type anymore.

Signed-off-by: Heesub Shin <heesub.shin@samsung.com>
Reviewed-by: Mitchel Humpherys <mitchelh@codeaurora.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>