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/board/mousse/u-boot.lds b/board/mousse/u-boot.lds
index 4cfb95c..ef73e2b 100644
--- a/board/mousse/u-boot.lds
+++ b/board/mousse/u-boot.lds
@@ -85,6 +85,6 @@
    . = ALIGN(4);
   }
 
-  _end = . ;
+  __bss_end__ = . ;
   PROVIDE (end = .);
 }
diff --git a/board/mousse/u-boot.lds.ram b/board/mousse/u-boot.lds.ram
index 449d064..b3364be 100644
--- a/board/mousse/u-boot.lds.ram
+++ b/board/mousse/u-boot.lds.ram
@@ -99,6 +99,6 @@
     common/env_embedded.o (.ppcenv)
   } > ram
 
-  _end = . ;
+  __bss_end__ = . ;
   PROVIDE (end = .);
 }
diff --git a/board/mousse/u-boot.lds.rom b/board/mousse/u-boot.lds.rom
index 4f42b32..b4b9e02 100644
--- a/board/mousse/u-boot.lds.rom
+++ b/board/mousse/u-boot.lds.rom
@@ -126,6 +126,6 @@
    *(COMMON)
   }
 
-  _end = . ;
+  __bss_end__ = . ;
   PROVIDE (end = .);
 }