blk: Switch over to using uclass IDs

We currently have an if_type (interface type) and a uclass id. These are
closely related and we don't need to have both.

Drop the if_type values and use the uclass ones instead.

Maintain the existing, subtle, one-way conversion between UCLASS_USB and
UCLASS_MASS_STORAGE for now, and add a comment.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/tee/optee/rpmb.c b/drivers/tee/optee/rpmb.c
index cf5e0a0..5bc1375 100644
--- a/drivers/tee/optee/rpmb.c
+++ b/drivers/tee/optee/rpmb.c
@@ -48,7 +48,7 @@
 	if (!priv->rpmb_mmc)
 		return;
 
-	rc = blk_select_hwpart_devnum(IF_TYPE_MMC, priv->rpmb_dev_id,
+	rc = blk_select_hwpart_devnum(UCLASS_MMC, priv->rpmb_dev_id,
 				      priv->rpmb_original_part);
 	if (rc)
 		debug("%s: blk_select_hwpart_devnum() failed: %d\n",
@@ -88,7 +88,7 @@
 
 	priv->rpmb_original_part = mmc_get_blk_desc(mmc)->hwpart;
 
-	rc = blk_select_hwpart_devnum(IF_TYPE_MMC, dev_id, MMC_PART_RPMB);
+	rc = blk_select_hwpart_devnum(UCLASS_MMC, dev_id, MMC_PART_RPMB);
 	if (rc) {
 		debug("Device id %d: cannot select RPMB partition: %d\n",
 		      dev_id, rc);