iommu/ipmmu-vmsa: Document R-Car V3H and E3 IPMMU DT bindings

Update the IPMMU DT binding documentation to include the compat strings
for the IPMMU devices included in the R-Car V3H and E3 SoCs.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Joerg Roedel <jroedel@suse.de>