gpu: ion: tegra: add tegra custom ioctl handling.

Add tegra specific custom ioctl handling.

Change-Id: If87b47f969fe0b3fdbb3bee965c370f6610fd4be
Signed-off-by: Krishna Reddy <vdumpa@nvidia.com>
Reviewed-on: http://git-master/r/71113
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Hiroshi Doyu <hdoyu@nvidia.com>
Tested-by: Hiroshi Doyu <hdoyu@nvidia.com>