gpu: ion: Export ion_client_create

Will enable modules to allocate memory with ion.

Change-Id: I2e99e34758dbd1a43d2752e9801376215dc8d257
Signed-off-by: Johan Mossberg <johan.mossberg@stericsson.com>
Git-commit: 886996690b49c82bcc91865121d68fc767aeae2a
Git-repo: https://android.googlesource.com/kernel/common


Signed-off-by: Laura Abbott <lauraa@codeaurora.org>