Revert "gpu: ion: repurpose flags field for heap_mask and caching"

This reverts commit 4334740161b19e5d736796f839c4aaa5964b74c7.
Revert "gpu: ion: move msm-specific ioctls to custom_ioctl"

This reverts commit 719aa810d7d3d9dcf36d879103ada5a3aa9ff8f8.
Revert "msm: ion: Only return Ion flags in ion_handle_get_flags"

This reverts commit 92e841512949ec7f5f9d6079082ec818649c9864.