RISC-V: Build Infrastructure

This patch contains all the build infrastructure that actually enables
the RISC-V port.  This includes Makefiles, linker scripts, and Kconfig
files.  It also contains the only top-level change, which adds RISC-V to
the list of architectures that need a sed run to produce the ARCH
variable when building locally.

Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
diff --git a/Makefile b/Makefile
index d111994..08ffcb1 100644
--- a/Makefile
+++ b/Makefile
@@ -225,7 +225,8 @@
 				  -e s/arm.*/arm/ -e s/sa110/arm/ \
 				  -e s/s390x/s390/ -e s/parisc64/parisc/ \
 				  -e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
-				  -e s/sh[234].*/sh/ -e s/aarch64.*/arm64/ )
+				  -e s/sh[234].*/sh/ -e s/aarch64.*/arm64/ \
+				  -e s/riscv.*/riscv/)
 
 # Cross compiling and selecting different set of gcc/bin-utils
 # ---------------------------------------------------------------------------