nios2: Build infrastructure

This patch adds Makefile and Kconfig files required for building a
nios2 kernel.

Signed-off-by: Ley Foon Tan <lftan@altera.com>
diff --git a/arch/nios2/platform/Makefile b/arch/nios2/platform/Makefile
new file mode 100644
index 0000000..46364f1
--- /dev/null
+++ b/arch/nios2/platform/Makefile
@@ -0,0 +1 @@
+obj-y += platform.o