global: Use CONFIG_XPL_BUILD instead of CONFIG_SPL_BUILD

Complete this rename for all directories outside arch/ board/ drivers/
and include/

Use the new symbol to refer to any 'SPL' build, including TPL and VPL

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/dts/Makefile b/dts/Makefile
index d6c2c9d..62a6568 100644
--- a/dts/Makefile
+++ b/dts/Makefile
@@ -53,7 +53,7 @@
 arch-dtbs:
 	$(Q)$(MAKE) $(build)=$(dt_dir) dtbs
 
-ifeq ($(CONFIG_SPL_BUILD),y)
+ifeq ($(CONFIG_XPL_BUILD),y)
 obj-$(CONFIG_OF_EMBED) := dt-spl.dtb.o
 # support "out-of-tree" build for dtb-spl
 $(obj)/dt-spl.dtb.o: $(obj)/dt-spl.dtb.S FORCE