drm/i915/gem: Adjust vma offset for framebuffer mmap offset

When mapping a framebuffer object, the virtual memory area (VMA)
offset ('vm_pgoff') should be adjusted by the start of the
'vma_node' associated with the object. This ensures that the VMA
offset is correctly aligned with the corresponding offset within
the GGTT aperture.

Increment vm_pgoff by the start of the vma_node with the offset=
provided by the user.

Suggested-by: Chris Wilson <chris.p.wilson@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: <stable@vger.kernel.org> # v4.9+
[Joonas: Add Cc: stable]
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240802083850.103694-2-andi.shyti@linux.intel.com


(cherry picked from commit 60a2066c)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>