mmc: Add more debugging for SPL

When MMC booting fails it is sometimes hard to figure out what went
wrong as there is no error code. It isn't even clear which MMC device
was chosen, since SPL can have its own numbering.

Add some debugging to help with this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl_mmc.c b/common/spl/spl_mmc.c
index 1337596..1f69659 100644
--- a/common/spl/spl_mmc.c
+++ b/common/spl/spl_mmc.c
@@ -50,6 +50,7 @@
 	ret = spl_load(spl_image, bootdev, &load, 0, sector << bd->log2blksz);
 	if (ret) {
 		puts("mmc_load_image_raw_sector: mmc block read error\n");
+		log_debug("(error=%d)\n", ret);
 		return ret;
 	}
 
@@ -76,6 +77,12 @@
 	int ret;
 
 #if CONFIG_IS_ENABLED(DM_MMC)
+	struct udevice *dev;
+	struct uclass *uc;
+
+	log_debug("Selecting MMC dev %d; seqs:\n", mmc_dev);
+	uclass_id_foreach_dev(UCLASS_MMC, dev, uc)
+		log_debug("%d: %s\n", dev_seq(dev), dev->name);
 	ret = mmc_init_device(mmc_dev);
 #else
 	ret = mmc_initialize(NULL);
@@ -91,6 +98,9 @@
 		       mmc_dev, ret);
 		return ret;
 	}
+#if CONFIG_IS_ENABLED(DM_MMC)
+	log_debug("mmc %d: %s\n", mmc_dev, (*mmcp)->dev->name);
+#endif
 
 	return 0;
 }
@@ -342,6 +352,8 @@
 
 	/* Perform peripheral init only once for an mmc device */
 	mmc_dev = spl_mmc_get_device_index(bootdev->boot_device);
+	log_debug("boot_device=%d, mmc_dev=%d\n", bootdev->boot_device,
+		  mmc_dev);
 	if (!mmc || spl_mmc_get_mmc_devnum(mmc) != mmc_dev) {
 		ret = spl_mmc_find_device(&mmc, mmc_dev);
 		if (ret)