spl: Drop the switch() statement for OS selection

This code is pretty ugly, with many #ifdefs

There are quite a lot of IH_OS_U_BOOT values so the compiler struggles
to create a jump table here. Also, most of the options are normally
disabled.

Change it to an else...if construct instead. Add an accessor for the
spl_image field behind an #ifdef to avoid needing #ifdef in the C code.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/spl.h

@@ -263,6 +263,15 @@ struct spl_image_info {
 #endif
 };
 
+static inline void *spl_image_fdt_addr(struct spl_image_info *info)
+{
+#if CONFIG_IS_ENABLED(LOAD_FIT) || CONFIG_IS_ENABLED(LOAD_FIT_FULL)
+	return info->fdt_addr;
+#else
+	return 0;
+#endif
+}
+
 /**
  * Information required to load data from a device
  *