arch: Use CONFIG_XPL_BUILD instead of CONFIG_SPL_BUILD

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/arch/arm/mach-zynq/Makefile b/arch/arm/mach-zynq/Makefile
index d9b2b99..8545331 100644
--- a/arch/arm/mach-zynq/Makefile
+++ b/arch/arm/mach-zynq/Makefile
@@ -12,4 +12,4 @@
 obj-y	+= clk.o
 obj-y	+= lowlevel_init.o
 AFLAGS_lowlevel_init.o := -mfpu=neon
-obj-$(CONFIG_SPL_BUILD)	+= spl.o ps7_spl_init.o
+obj-$(CONFIG_XPL_BUILD)	+= spl.o ps7_spl_init.o