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/esd/pmc440/u-boot-nand.lds b/board/esd/pmc440/u-boot-nand.lds
index ca7df45..101b893 100644
--- a/board/esd/pmc440/u-boot-nand.lds
+++ b/board/esd/pmc440/u-boot-nand.lds
@@ -129,6 +129,6 @@
    . = ALIGN(4);
   }
 
-  __bss_end__ = . ;
+  __bss_end = . ;
   PROVIDE (end = .);
 }