drm/exynos: added missed vm area region mapping type.

with this patch, if the memory region is physically non-continuous
then VM_MIXEDMAP is set to vm->vm_flags otherwise VM_PFNMAP.
we had missed this flag setting.
Signed-off-by: NInki Dae <inki.dae@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_gem.c

@@ -514,6 +514,8 @@ static int exynos_drm_gem_mmap_buffer(struct file *filp,
 		if (!buffer->pages)
 			return -EINVAL;
 
+		vma->vm_flags |= VM_MIXEDMAP;
+
 		do {
 			ret = vm_insert_page(vma, uaddr, buffer->pages[i++]);
 			if (ret) {