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/armv7/socfpga/u-boot-spl.lds b/arch/arm/cpu/armv7/socfpga/u-boot-spl.lds
index a7c9c9d..4282beb 100644
--- a/arch/arm/cpu/armv7/socfpga/u-boot-spl.lds
+++ b/arch/arm/cpu/armv7/socfpga/u-boot-spl.lds
@@ -28,7 +28,11 @@
 
 	. = ALIGN(4);
 	__image_copy_end = .;
-	_end = .;
+
+	.end :
+	{
+		*(.__end)
+	}
 
 	.bss : {
 		. = ALIGN(4);