RISC-V: drop SOC_SIFIVE for ARCH_SIFIVE

All the users in the kernel are gone and generated .config files from
previous LTS kernels will contain ARCH_SIFIVE. Drop SOC_SIFIVE and
update the defconfig.
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

arch/riscv/Kconfig.socs

@@ -14,9 +14,6 @@ config ARCH_RENESAS
 	  This enables support for the RISC-V based Renesas SoCs.
 
 config ARCH_SIFIVE
-	def_bool SOC_SIFIVE
-
-config SOC_SIFIVE
 	bool "SiFive SoCs"
 	select ERRATA_SIFIVE if !XIP_KERNEL
 	help

arch/riscv/configs/defconfig

@@ -27,7 +27,7 @@ CONFIG_EXPERT=y
 CONFIG_PROFILING=y
 CONFIG_ARCH_MICROCHIP=y
 CONFIG_ARCH_RENESAS=y
-CONFIG_SOC_SIFIVE=y
+CONFIG_ARCH_SIFIVE=y
 CONFIG_ARCH_SOPHGO=y
 CONFIG_SOC_STARFIVE=y
 CONFIG_ARCH_SUNXI=y