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

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Walmsley <redacted>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: linux-riscv@lists.infradead.org

  arch/riscv/Makefile              |   10 ++++++++++
  arch/riscv/configs/32-bit.config |    2 ++
  arch/riscv/configs/64-bit.config |    2 ++
  3 files changed, 14 insertions(+)

--- linux-next-20210715.orig/arch/riscv/Makefile
+++ linux-next-20210715/arch/riscv/Makefile

@@ -132,3 +132,13 @@ zinstall install:
  
  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
--- /dev/null
+++ linux-next-20210715/arch/riscv/configs/32-bit.config

@@ -0,0 +1,2 @@
+CONFIG_ARCH_RV32I=y
+CONFIG_32BIT=y
--- /dev/null
+++ linux-next-20210715/arch/riscv/configs/64-bit.config

@@ -0,0 +1,2 @@
+CONFIG_ARCH_RV64I=y
+CONFIG_64BIT=y