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>

cmd/ide.c

@@ -37,7 +37,7 @@ int do_ide(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
 		}
 	}
 
-	return blk_common_cmd(argc, argv, IF_TYPE_IDE, &curr_device);
+	return blk_common_cmd(argc, argv, UCLASS_IDE, &curr_device);
 }
 
 int do_diskboot(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])