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/arch/arm/cpu/arm1136/u-boot-spl.lds b/arch/arm/cpu/arm1136/u-boot-spl.lds
index bccde73..0299902 100644
--- a/arch/arm/cpu/arm1136/u-boot-spl.lds
+++ b/arch/arm/cpu/arm1136/u-boot-spl.lds
@@ -33,7 +33,11 @@
 	.data : { *(SORT_BY_ALIGNMENT(.data*)) } >.sram
 	. = ALIGN(4);
 	__image_copy_end = .;
-	_end = .;
+
+	.end :
+	{
+		*(.__end)
+	}
 
 	.bss :
 	{