drivers: 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/drivers/ddr/imx/phy/Makefile b/drivers/ddr/imx/phy/Makefile
index bb3d4ee..592d0c6 100644
--- a/drivers/ddr/imx/phy/Makefile
+++ b/drivers/ddr/imx/phy/Makefile
@@ -4,6 +4,6 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-ifdef CONFIG_SPL_BUILD
+ifdef CONFIG_XPL_BUILD
 obj-$(CONFIG_IMX_SNPS_DDR_PHY) += helper.o ddrphy_utils.o ddrphy_train.o ddrphy_csr.o
 endif