gpu: ion: Add EXPORT_SYMBOL to functions

Several functions in the ion interface is missing
EXPORT_SYMBOL. This is needed to allow clients to
use these functions from kernel modules.

Add EXPORT_SYMBOL to functions that are supposed
to be exposed.

Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
[jstultz: modified patch to apply to staging directory]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>