Fix for new ARC toolchain

In order to use upstream buildroot to build the latest ARC toolchain with
kernel/skids headers, we need to export arch/arc/include/asm/page.h.

Change-Id: Ice10de6213e7f9481f2d9df96b2120e5c16c1d47
diff --git a/arch/arc/include/asm/Kbuild b/arch/arc/include/asm/Kbuild
index c68e168..46e2f86 100644
--- a/arch/arc/include/asm/Kbuild
+++ b/arch/arc/include/asm/Kbuild
@@ -1 +1,2 @@
 include include/asm-generic/Kbuild.asm
+header-y += page.h