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>

include/blk.h

@@ -7,6 +7,7 @@
 #ifndef BLK_H
 #define BLK_H
 
+#include <dm/uclass-id.h>
 #include <efi.h>
 
 #ifdef CONFIG_SYS_64BIT_LBA
@@ -27,22 +28,7 @@ static inline bool blk_enabled(void)
 }
 
 /* Interface types: */
-enum if_type {
-	IF_TYPE_UNKNOWN = 0,
-	IF_TYPE_IDE,
-	IF_TYPE_SCSI,
-	IF_TYPE_USB,
-	IF_TYPE_MMC,
-	IF_TYPE_SATA,
-	IF_TYPE_HOST,
-	IF_TYPE_NVME,
-	IF_TYPE_EFI_LOADER,
-	IF_TYPE_PVBLOCK,
-	IF_TYPE_VIRTIO,
-	IF_TYPE_EFI_MEDIA,
-
-	IF_TYPE_COUNT,			/* Number of interface types */
-};
+#define if_type uclass_id
 
 #define BLK_VEN_SIZE		40
 #define BLK_PRD_SIZE		20

include/mmc.h

@@ -767,7 +767,7 @@ struct mmc *mmc_create(const struct mmc_config *cfg, void *priv);
 /**
  * mmc_bind() - Set up a new MMC device ready for probing
  *
- * A child block device is bound with the IF_TYPE_MMC interface type. This
+ * A child block device is bound with the UCLASS_MMC interface type. This
  * allows the device to be used with CONFIG_BLK
  *
  * @dev:	MMC device to set up