iommu/ipmmu-vmsa: Add r8a779(70|95) DT bindings

Update the IPMMU DT binding documentation to include the
r8a77970 (R-Car V3M) and r8a77995 (R-Car D3) compat strings.

Based on work for r8a7796 by Magnus Damm.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
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v2
* Add reviewed-by tag from Geert Uytterhoeven