Revert "gpu: ion: Add support for getting the heap size of CMA regions"

This reverts commit 38cb3431ac04141ca3e426c38f668281fa71fed5.
Revert "gpu: ion: Add ioctls for prefetching/draining pools"

This reverts commit 11c322ac57b3cf6c2dd4f07a2817af108f3cfc32.