gpu: nvgpu: Add common vaddr translate function

Add a function to do address translation for IOMMU capable GPUs.
When an iGPU is behind and IOMMU it can pick whether to use that
IOMMU for translation by adding a bit to physical addresses. This
function takes care of that.

However, this required an abstracted nvgpu_iommuable() API to
check whether a GPU is behind an IOMMU. This patch adds that API
for Linux.

JIRA NVGPU-68

Change-Id: I489d14475167c019c294407372395df78c8b5feb
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1542965
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: svc-mobile-coverity <svc-mobile-coverity@nvidia.com>
Reviewed-by: svccoveritychecker <svccoveritychecker@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Sourab Gupta <sourabg@nvidia.com>
Reviewed-by: Konsta Holtta <kholtta@nvidia.com>
Reviewed-by: Vijayakumar Subbu <vsubbu@nvidia.com>

drivers/gpu/nvgpu/common/linux/dma.c

@@ -631,3 +631,10 @@ void nvgpu_free_sgtable(struct gk20a *g, struct sg_table **sgt)
 	nvgpu_kfree(g, *sgt);
 	*sgt = NULL;
 }
+
+bool nvgpu_iommuable(struct gk20a *g)
+{
+	struct nvgpu_os_linux *l = nvgpu_os_linux_from_gk20a(g);
+
+	return device_is_iommuable(l->dev);
+}