arc: Make u-boot-arc.h a private header

Rather than including this arch-specific header file in common.h, include
it from within arc's u-boot.h header.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arc/include/asm/u-boot.h b/arch/arc/include/asm/u-boot.h
index e354edf..0454872 100644
--- a/arch/arc/include/asm/u-boot.h
+++ b/arch/arc/include/asm/u-boot.h
@@ -8,6 +8,7 @@
 #define __ASM_ARC_U_BOOT_H__
 
 #include <asm-generic/u-boot.h>
+#include <asm/u-boot-arc.h>
 
 /* For image.h:image_check_target_arch() */
 #define IH_ARCH_DEFAULT IH_ARCH_ARC
diff --git a/include/common.h b/include/common.h
index 4707686..b07b8fc 100644
--- a/include/common.h
+++ b/include/common.h
@@ -445,7 +445,7 @@
 # include <asm/u-boot-mips.h>
 #endif /* CONFIG_MIPS */
 #ifdef CONFIG_ARC
-# include <asm/u-boot-arc.h>
+# include <asm/u-boot.h>
 #endif /* CONFIG_ARC */
 
 #ifdef CONFIG_AUTO_COMPLETE