ion: export functions to enable usage by kernel modules

ion: export functions to enable usage by kernel modules

BZ:32709

EXPORT_SYMBOL/EXPORT_SYMBOL_GPL is missing for the exposed ION
API. This patch adds the EXPORT_SYMBOL to the public ION API.

Change-Id: I88ff618506efd136eb1d1b2648edfb4cea4ae53d
Signed-off-by: Jianxu Zheng <jian.xu.zheng@intel.com>
Reviewed-on: http://android.intel.com:8080/44095
Reviewed-by: Wang, Wen W <wen.w.wang@intel.com>
Reviewed-by: Gross, Mark <mark.gross@intel.com>
Tested-by: Ng, Cheon-woei <cheon-woei.ng@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>