Replace __bss_end__ with __bss_end

Note this is a tree-wide change affecting multiple architectures.

At present we use __bss_start, but mostly __bss_end__. This seems
inconsistent and in a number of places __bss_end is used instead.

Change to use __bss_end for the BSS end symbol throughout U-Boot. This
makes it possible to use the asm-generic/sections.h file on all
archs.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/altera/nios2-generic/u-boot.lds b/board/altera/nios2-generic/u-boot.lds
index 289386b..bf7600a 100644
--- a/board/altera/nios2-generic/u-boot.lds
+++ b/board/altera/nios2-generic/u-boot.lds
@@ -102,7 +102,7 @@
 	  *(.scommon)
 	}
 	. = ALIGN(4);
-	__bss_end__ = .;
+	__bss_end = .;
 	PROVIDE (end = .);
 
 	/* DEBUG -- symbol table, string table, etc. etc.