iommu/renesas: Update help description for IPMMU_VMSA config

ipmmu-vmsa driver is also used on Renesas RZ/G{1,2} Soc's, update the
same to reflect the help description for IPMMU_VMSA config.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200911101912.20701-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>