exynos-mem: Fix major security hole
This fixes the exynos-mem device security hole. The driver allowed any user
to access all of the device's lowmem through the provided mmap functionality.

We create a small little framework collecting the actual CMA memory blocks
that exist on the device; they are the root cause of the existence of this device
driver. We white-list only the CMA memory spaces as parameters to the mmap
function and deny access to any other memory space requests.

We furthermore just allow access to the "s3c-fimc" memory block as this is
seemingly the only space which upon access denial actually breaks functionality.

This patch was modified to be suitable for Exynos 4210 by
Andrew Dodd <atd7@cornell.edu> from Andrei's original Exynos 4412 patch.

https://github.com/EpicAOSP/android_kernel_samsung_smdk4210_new/commit/5b622102eb2787b71a71488bd29d7be921431c37

Change-Id: Ibc5f248a2175634bff835c9ab8c10cec8bdac7e4