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-lpc32xx/Makefile b/arch/arm/mach-lpc32xx/Makefile
index 6303570..f551abb 100644
--- a/arch/arm/mach-lpc32xx/Makefile
+++ b/arch/arm/mach-lpc32xx/Makefile
@@ -5,4 +5,4 @@
 
 obj-y   = cpu.o clk.o devices.o timer.o
 
-obj-$(CONFIG_SPL_BUILD) += dram.o lowlevel_init.o
+obj-$(CONFIG_XPL_BUILD) += dram.o lowlevel_init.o