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/arm/cpu/arm920t/ep93xx/u-boot.lds b/arch/arm/cpu/arm920t/ep93xx/u-boot.lds
index 5bfcb02..4cc82a5 100644
--- a/arch/arm/cpu/arm920t/ep93xx/u-boot.lds
+++ b/arch/arm/cpu/arm920t/ep93xx/u-boot.lds
@@ -55,5 +55,5 @@
 	. = ALIGN(4);
 	__bss_start = .;
 	.bss : { *(.bss) }
-	_end = .;
+	__bss_end__ = .;
 }