dt-bindings: iommu: ipmmu-vmsa: Add device tree support for r8a774[35]

Document r8a774[35] specific compatible strings. The Renesas RZ/G1[ME]
(r8a774[35]) IPMMU are identical to the R-Car Gen2 family.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Chris Paterson <chris.paterson2@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Joerg Roedel <jroedel@suse.de>