arm bootm: Allow to pass board specified atags

Board can implement function setup_board_tags which is used for adding atags

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
diff --git a/arch/arm/include/asm/setup.h b/arch/arm/include/asm/setup.h
index 89df4dc..78a7fac 100644
--- a/arch/arm/include/asm/setup.h
+++ b/arch/arm/include/asm/setup.h
@@ -267,3 +267,8 @@
 extern struct meminfo meminfo;
 
 #endif
+
+/*
+ * Board specified tags
+ */
+void setup_board_tags(struct tag **in_params);