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/riscv/lib/Makefile b/arch/riscv/lib/Makefile
index 65dc49f..3bc34cd 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -24,7 +24,7 @@
 endif
 obj-y   += setjmp.o
 obj-$(CONFIG_$(SPL_)SMP) += smp.o
-obj-$(CONFIG_SPL_BUILD)	+= spl.o
+obj-$(CONFIG_XPL_BUILD)	+= spl.o
 obj-y   += fdt_fixup.o
 obj-$(CONFIG_$(SPL)CMD_BDI) += bdinfo.o