Document RZ/G1H (R8A7742) SoC bindings.

No driver change is needed due to the fallback compatible value
"renesas,ipmmu-vmsa".
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200825141805.27105-2-prabhakar.mahadev-lad.rj@bp.renesas.comSigned-off-by: Joerg Roedel <jroedel@suse.de>