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_mmc.c b/common/spl/spl_mmc.c
index 32d7c2a..85e3de8 100644
--- a/common/spl/spl_mmc.c
+++ b/common/spl/spl_mmc.c
@@ -355,6 +355,6 @@
 	return err;
 }
 
-SPL_LOAD_IMAGE_METHOD(0, BOOT_DEVICE_MMC1, spl_mmc_load_image);
-SPL_LOAD_IMAGE_METHOD(0, BOOT_DEVICE_MMC2, spl_mmc_load_image);
-SPL_LOAD_IMAGE_METHOD(0, BOOT_DEVICE_MMC2_2, spl_mmc_load_image);
+SPL_LOAD_IMAGE_METHOD("MMC1", 0, BOOT_DEVICE_MMC1, spl_mmc_load_image);
+SPL_LOAD_IMAGE_METHOD("MMC2", 0, BOOT_DEVICE_MMC2, spl_mmc_load_image);
+SPL_LOAD_IMAGE_METHOD("MMC2_2", 0, BOOT_DEVICE_MMC2_2, spl_mmc_load_image);