staging: ion: remove order from struct page_info

ION system heap uses an internal data structure, struct page_info, for
tracking down the meta information of the pages allocated from the pool.
Now that the pool returns compound pages, we don't need to store page
order in struct page_info.

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>