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>

arch/riscv/lib/Makefile

@@ -0,0 +1,6 @@
+lib-y	+= delay.o
+lib-y	+= memcpy.o
+lib-y	+= memset.o
+lib-y	+= uaccess.o
+
+lib-$(CONFIG_32BIT) += udivdi3.o