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/powerpc/cpu/mpc83xx/start.S b/arch/powerpc/cpu/mpc83xx/start.S
index 460ac9a..7e60315 100644
--- a/arch/powerpc/cpu/mpc83xx/start.S
+++ b/arch/powerpc/cpu/mpc83xx/start.S
@@ -72,7 +72,7 @@
 	START_GOT
 	GOT_ENTRY(_GOT2_TABLE_)
 	GOT_ENTRY(__bss_start)
-	GOT_ENTRY(_end)
+	GOT_ENTRY(__bss_end__)
 
 #ifndef CONFIG_NAND_SPL
 	GOT_ENTRY(_FIXUP_TABLE_)
@@ -977,7 +977,7 @@
 	 */
 	lwz	r4,GOT(environment)
 #else
-	lwz	r4,GOT(_end)
+	lwz	r4,GOT(__bss_end__)
 #endif
 
 	cmplw	0, r3, r4