arm64: Add NOLOAD attribute NOLOAD to .bss sections

Mark explicitly bss sections to not be loaded at
run time.
The similar patch was done in past by:
"Fix linker scripts: add NOLOAD atribute to .bss/.sbss sections"
(sha1: 64134f0112)

The problem is related to latest toolchain added to Xilinx
v2017.1 design tools where jtag loader is trying to access
ununitialized memory.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/cpu/armv8/u-boot-spl.lds

@@ -56,17 +56,17 @@ SECTIONS
 
 	_image_binary_end = .;
 
-	.bss_start : {
+	.bss_start (NOLOAD) : {
 		. = ALIGN(8);
 		KEEP(*(.__bss_start));
 	} >.sdram
 
-	.bss : {
+	.bss (NOLOAD) : {
 		*(.bss*)
 		 . = ALIGN(8);
 	} >.sdram
 
-	.bss_end : {
+	.bss_end (NOLOAD) : {
 		KEEP(*(.__bss_end));
 	} >.sdram