libfdt: Bring in upstream stringlist functions

These have now landed upstream. The naming is different and in one case the
function signature has changed. Update the code to match.

This applies the following upstream commits by
Thierry Reding <treding@nvidia.com> :

   604e61e fdt: Add functions to retrieve strings
   8702bd1 fdt: Add a function to get the index of a string
   2218387 fdt: Add a function to count strings

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/image-fit.c b/common/image-fit.c
index 1b0234a..d67678a 100644
--- a/common/image-fit.c
+++ b/common/image-fit.c
@@ -1457,7 +1457,7 @@
 void fit_conf_print(const void *fit, int noffset, const char *p)
 {
 	char *desc;
-	char *uname;
+	const char *uname;
 	int ret;
 	int loadables_index;
 
@@ -1469,7 +1469,7 @@
 	else
 		printf("%s\n", desc);
 
-	uname = (char *)fdt_getprop(fit, noffset, FIT_KERNEL_PROP, NULL);
+	uname = fdt_getprop(fit, noffset, FIT_KERNEL_PROP, NULL);
 	printf("%s  Kernel:       ", p);
 	if (uname == NULL)
 		printf("unavailable\n");
@@ -1477,26 +1477,23 @@
 		printf("%s\n", uname);
 
 	/* Optional properties */
-	uname = (char *)fdt_getprop(fit, noffset, FIT_RAMDISK_PROP, NULL);
+	uname = fdt_getprop(fit, noffset, FIT_RAMDISK_PROP, NULL);
 	if (uname)
 		printf("%s  Init Ramdisk: %s\n", p, uname);
 
-	uname = (char *)fdt_getprop(fit, noffset, FIT_FDT_PROP, NULL);
+	uname = fdt_getprop(fit, noffset, FIT_FDT_PROP, NULL);
 	if (uname)
 		printf("%s  FDT:          %s\n", p, uname);
 
-	uname = (char *)fdt_getprop(fit, noffset, FIT_FPGA_PROP, NULL);
+	uname = fdt_getprop(fit, noffset, FIT_FPGA_PROP, NULL);
 	if (uname)
 		printf("%s  FPGA:         %s\n", p, uname);
 
 	/* Print out all of the specified loadables */
 	for (loadables_index = 0;
-	     fdt_get_string_index(fit, noffset,
-			FIT_LOADABLE_PROP,
-			loadables_index,
-			(const char **)&uname) == 0;
-	     loadables_index++)
-	{
+	     uname = fdt_stringlist_get(fit, noffset, FIT_LOADABLE_PROP,
+					loadables_index, NULL), uname;
+	     loadables_index++) {
 		if (loadables_index == 0) {
 			printf("%s  Loadables:    ", p);
 		} else {