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/MAINTAINERS b/MAINTAINERS
index 9b4b63b..754db55 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -423,6 +423,13 @@
 T:	git git://git.denx.de/u-boot-onenand.git
 F:	drivers/mtd/onenand/
 
+RISC-V
+M:	Rick Chen <rick@andestech.com>
+S:	Maintained
+T:	git git://git.denx.de/u-boot-riscv.git
+F:	arch/riscv/
+F:	tools/prelink-riscv.c
+
 SANDBOX
 M:	Simon Glass <sjg@chromium.org>
 S:	Maintained