x86: spl: Make moving BSS conditional

At present BSS is always placed in SDRAM. If a separate BSS is not in use
this means that BSS doesn't work as expected. Make the setting conditional
on the SEPARATE_BSS option.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/cpu/u-boot-spl.lds

@@ -57,7 +57,9 @@ SECTIONS
 
         _image_binary_end = .;
 
+#if CONFIG_IS_ENABLED(SEPARATE_BSS)
 	. = 0x120000;
+#endif
 	.bss (OVERLAY) : {
 		__bss_start = .;
 		*(.bss*)