staging: ion: remove struct ion_page_pool_item

The page pool uses an internal data structure, ion_page_pool_item, for
wrapping pooled pages and constructing a list. As the struct page
already provides ways for doing exactly the same thing, we do not need
to reinvent the wheel. This commit removes the data structure and slab
allocations for it.

Change-Id: I3653a71337abc26c0cd6791be7cb175055281036
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>
Git-commit: 38c003b113ceab37f80d020999d3ec2cbf784da3
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Laura Abbott <lauraa@codeaurora.org>