spl: Add a name to the SPL load-image methods

It is useful to name each method so that we can print out this name when
using the method. Currently this happens using a separate function. In
preparation for unifying this, add a name to each method.

The name is only available if we have libcommon support (i.e can use
printf()).

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl_nor.c b/common/spl/spl_nor.c
index 6bfa399..d07ca84 100644
--- a/common/spl/spl_nor.c
+++ b/common/spl/spl_nor.c
@@ -71,4 +71,4 @@
 
 	return 0;
 }
-SPL_LOAD_IMAGE_METHOD(0, BOOT_DEVICE_NOR, spl_nor_load_image);
+SPL_LOAD_IMAGE_METHOD("NOR", 0, BOOT_DEVICE_NOR, spl_nor_load_image);