arm: make _end compiler-generated

This prevents references to _end from generating absolute
relocation records.

This change is binary invariant for ARM targets.

Signed-off-by: Albert ARIBAUD <albert.u.boot@aribaud.net>
diff --git a/board/vpac270/u-boot-spl.lds b/board/vpac270/u-boot-spl.lds
index b6fdde4..5dbf94e 100644
--- a/board/vpac270/u-boot-spl.lds
+++ b/board/vpac270/u-boot-spl.lds
@@ -54,7 +54,12 @@
 
 	. = ALIGN(0x800);
 
-	_end = .;
+	.end :
+	{
+		*(.__end)
+	}
+
+	_image_binary_end = .;
 
 	.bss __rel_dyn_start (OVERLAY) : {
 		__bss_start = .;
@@ -63,7 +68,7 @@
 		__bss_end = .;
 	}
 
-	.dynsym _end : { *(.dynsym) }
+	.dynsym _image_binary_end : { *(.dynsym) }
 	.dynbss : { *(.dynbss) }
 	.dynstr : { *(.dynstr*) }
 	.dynamic : { *(.dynamic*) }