dt-bindings: iommu/ipmmu-vmsa: Add R-Car M3-N (R8A77965)

Add Renesas R-Car M3-N (R8A77965) compat string to IPMMU DT bindings
documentation.

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Joerg Roedel <jroedel@suse.de>