xpl: Rename spl_phase() to xpl_phase()

Rename this function to indicate that it refers to any xPL phase.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/cpu/apollolake/pch.c b/arch/x86/cpu/apollolake/pch.c
index 3219031..07ef26f 100644
--- a/arch/x86/cpu/apollolake/pch.c
+++ b/arch/x86/cpu/apollolake/pch.c
@@ -12,7 +12,7 @@
 
 static int apl_set_spi_protect(struct udevice *dev, bool protect)
 {
-	if (spl_phase() == PHASE_SPL)
+	if (xpl_phase() == PHASE_SPL)
 		return lpc_set_spi_protect(dev, BIOS_CTRL, protect);
 
 	return 0;