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/ram/Makefile b/drivers/ram/Makefile
index fdb2e78..35d8f57 100644
--- a/drivers/ram/Makefile
+++ b/drivers/ram/Makefile
@@ -20,7 +20,7 @@
 obj-$(CONFIG_IMXRT_SDRAM) += imxrt_sdram.o
 
 obj-$(CONFIG_RAM_SIFIVE) += sifive/
-ifdef CONFIG_SPL_BUILD
+ifdef CONFIG_XPL_BUILD
 obj-$(CONFIG_SPL_STARFIVE_DDR) += starfive/
 endif