rename _end to __bss_end__

Currently, _end is used for end of BSS section.  We want _end to mean
end of u-boot image, so we rename _end to __bss_end__ first.

Signed-off-by: Po-Yu Chuang <ratbert@faraday-tech.com>
diff --git a/arch/sh/cpu/sh3/u-boot.lds b/arch/sh/cpu/sh3/u-boot.lds
index 2716246..9bf8503 100644
--- a/arch/sh/cpu/sh3/u-boot.lds
+++ b/arch/sh/cpu/sh3/u-boot.lds
@@ -98,5 +98,5 @@
 	}
 	PROVIDE (bss_end = .);
 
-	PROVIDE (_end = .);
+	PROVIDE (__bss_end__ = .);
 }