arm: Use sections header to obtain link symbols

Include this header to get access to link symbols, which are otherwise
removed.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/lib/board.c b/arch/arm/lib/board.c
index 162e2cc..0521178 100644
--- a/arch/arm/lib/board.c
+++ b/arch/arm/lib/board.c
@@ -53,6 +53,7 @@
 #include <fdtdec.h>
 #include <post.h>
 #include <logbuff.h>
+#include <asm/sections.h>
 
 #ifdef CONFIG_BITBANGMII
 #include <miiphy.h>