drm/gpusvm: Use dma-map IOVA alloc, link, and sync API in GPU SVM

drm/gpusvm: Use dma-map IOVA alloc, link, and sync API in GPU SVM

The dma-map IOVA alloc, link, and sync APIs perform significantly better
than dma-map / dma-unmap, as they avoid costly IOMMU synchronizations.
This difference is especially noticeable when mapping a 2MB region in
4KB pages.

Use the IOVA alloc, link, and sync APIs for GPU SVM, which create DMA
mappings between the CPU and GPU.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patch.msgid.link/20260410205929.3914474-2-matthew.brost@intel.com