riscv: Add Kconfig to support RISC-V

Add Kconfig and makefile for RISC-V
Also modify MAINTAINERS for it.

Signed-off-by: Rick Chen <rick@andestech.com>
Signed-off-by: Rick Chen <rickchen36@gmail.com>
Signed-off-by: Greentime Hu <green.hu@gmail.com>
Cc: Padmarao Begari <Padmarao.Begari@microsemi.com>
diff --git a/arch/riscv/config.mk b/arch/riscv/config.mk
new file mode 100644
index 0000000..6b681c4
--- /dev/null
+++ b/arch/riscv/config.mk
@@ -0,0 +1,33 @@
+#
+# (C) Copyright 2000-2002
+# Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+#
+# Copyright (c) 2017 Microsemi Corporation.
+# Padmarao Begari, Microsemi Corporation <padmarao.begari@microsemi.com>
+#
+# Copyright (C) 2017 Andes Technology Corporation
+# Rick Chen, Andes Technology Corporation <rick@andestech.com>
+#
+# SPDX-License-Identifier:	GPL-2.0+
+
+ifeq ($(CROSS_COMPILE),)
+CROSS_COMPILE := riscv32-unknown-linux-gnu-
+endif
+
+32bit-emul		:= elf32lriscv
+64bit-emul		:= elf64lriscv
+
+ifdef CONFIG_32BIT
+PLATFORM_LDFLAGS	+= -m $(32bit-emul)
+endif
+
+ifdef CONFIG_64BIT
+PLATFORM_LDFLAGS	+= -m $(64bit-emul)
+endif
+
+CONFIG_STANDALONE_LOAD_ADDR = 0x00000000 \
+			      -T $(srctree)/examples/standalone/riscv.lds
+
+PLATFORM_CPPFLAGS	+= -ffixed-gp -fpic
+PLATFORM_RELFLAGS += -fno-strict-aliasing -fno-common -gdwarf-2
+LDFLAGS_u-boot += --gc-sections -static -pie