soc: renesas: Introduce ARCH_RCAR_GEN4

Currently, all Kconfig symbols for R-Car Gen4 SoCs select the
ARCH_RCAR_GEN3 SoC family symbol, which might confuse the casual reader.

Fix this by introducing a new SoC family symbol for R-Car Gen4 SoCs.
For now this just selects ARCH_RCAR_GEN3, to avoid duplication, and to
relax dependencies.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/a283913ba7a39ec2dae0ebf9fc2b06096f009511.1706194617.git.geert+renesas@glider.be

drivers/soc/renesas/Kconfig

@@ -34,6 +34,10 @@ config ARCH_RCAR_GEN3
 	select SYS_SUPPORTS_SH_CMT
 	select SYS_SUPPORTS_SH_TMU
 
+config ARCH_RCAR_GEN4
+	bool
+	select ARCH_RCAR_GEN3
+
 config ARCH_RMOBILE
 	bool
 	select PM
@@ -240,7 +244,7 @@ config ARCH_R8A77961
 
 config ARCH_R8A779F0
 	bool "ARM64 Platform support for R-Car S4-8"
-	select ARCH_RCAR_GEN3
+	select ARCH_RCAR_GEN4
 	select SYSC_R8A779F0
 	help
 	  This enables support for the Renesas R-Car S4-8 SoC.
@@ -261,14 +265,14 @@ config ARCH_R8A77970
 
 config ARCH_R8A779A0
 	bool "ARM64 Platform support for R-Car V3U"
-	select ARCH_RCAR_GEN3
+	select ARCH_RCAR_GEN4
 	select SYSC_R8A779A0
 	help
 	  This enables support for the Renesas R-Car V3U SoC.
 
 config ARCH_R8A779G0
 	bool "ARM64 Platform support for R-Car V4H"
-	select ARCH_RCAR_GEN3
+	select ARCH_RCAR_GEN4
 	select SYSC_R8A779G0
 	help
 	  This enables support for the Renesas R-Car V4H SoC.