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/m68k/lib/board.c b/arch/m68k/lib/board.c
index 7867ba5..f824b34 100644
--- a/arch/m68k/lib/board.c
+++ b/arch/m68k/lib/board.c
@@ -76,7 +76,7 @@
 #include <environment.h>
 
 extern ulong __init_end;
-extern ulong _end;
+extern ulong __bss_end__;
 
 extern	void timer_init(void);
 
@@ -252,7 +252,7 @@
 	 *	- monitor code
 	 *	- board info struct
 	 */
-	len = (ulong)&_end - CONFIG_SYS_MONITOR_BASE;
+	len = (ulong)&__bss_end__ - CONFIG_SYS_MONITOR_BASE;
 
 	addr = CONFIG_SYS_SDRAM_BASE + gd->ram_size;