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/lib/fdtdec.c b/lib/fdtdec.c
index 5edc8dd..ab05419 100644
--- a/lib/fdtdec.c
+++ b/lib/fdtdec.c
@@ -608,7 +608,7 @@
 static int fdtdec_prepare_fdt(const void *blob)
 {
 	if (!blob || ((uintptr_t)blob & 3) || fdt_check_header(blob)) {
-		if (spl_phase() <= PHASE_SPL) {
+		if (xpl_phase() <= PHASE_SPL) {
 			puts("Missing DTB\n");
 		} else {
 			printf("No valid device tree binary found at %p\n",