riscv: add rv32 and rv64 randconfig build targets

Add the ability to do randconfig build targets for both
rv32 and rv64.

Based on a similar patch by Michael Ellerman for PowerPC.

Usage:
  make ARCH=riscv rv32_randconfig
or
  make ARCH=riscv rv64_randconfig
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Makefile

@@ -140,3 +140,13 @@ install zinstall:
 
 archclean:
 	$(Q)$(MAKE) $(clean)=$(boot)
+
+PHONY += rv32_randconfig
+rv32_randconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/riscv/configs/32-bit.config \
+		-f $(srctree)/Makefile randconfig
+
+PHONY += rv64_randconfig
+rv64_randconfig:
+	$(Q)$(MAKE) KCONFIG_ALLCONFIG=$(srctree)/arch/riscv/configs/64-bit.config \
+		-f $(srctree)/Makefile randconfig

arch/riscv/configs/32-bit.config

+CONFIG_ARCH_RV32I=y
+CONFIG_32BIT=y

arch/riscv/configs/64-bit.config

+CONFIG_ARCH_RV64I=y
+CONFIG_64BIT=y