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_spi.c b/common/spl/spl_spi.c
index 78b8cd1..cd1d6b2 100644
--- a/common/spl/spl_spi.c
+++ b/common/spl/spl_spi.c
@@ -125,4 +125,4 @@
 	return err;
 }
 /* Use priorty 1 so that boards can override this */
-SPL_LOAD_IMAGE_METHOD(1, BOOT_DEVICE_SPI, spl_spi_load_image);
+SPL_LOAD_IMAGE_METHOD("SPI", 1, BOOT_DEVICE_SPI, spl_spi_load_image);