iommu/ipmmu-vmsa: Add support for R-Car Gen4

Add support for R-Car Gen4 like r8a779f0 (R-Car S4-8). The IPMMU
hardware design of r8a779f0 is the same as r8a779a0. So, rename
"r8a779a0" to "rcar_gen4".

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20220208002030.1319984-3-yoshihiro.shimoda.uh@renesas.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>