dm: blk: Convert interface type to an enum

Since these are sequentially numbered it makes sense to use an enum. It
avoids having to maintain the maximum value, and provides a type we can use
if it is useful.

In fact the maximum value is not used. Rename it to COUNT, since MAX suggests
it is the maximum valid value, but it is not.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Stephen Warren <swarren@nvidia.com>

include/blk.h

@@ -19,20 +19,23 @@ typedef ulong lbaint_t;
 #define LBAFU "%" LBAFlength "u"
 
 /* Interface types: */
-#define IF_TYPE_UNKNOWN		0
-#define IF_TYPE_IDE		1
-#define IF_TYPE_SCSI		2
-#define IF_TYPE_ATAPI		3
-#define IF_TYPE_USB		4
-#define IF_TYPE_DOC		5
-#define IF_TYPE_MMC		6
-#define IF_TYPE_SD		7
-#define IF_TYPE_SATA		8
-#define IF_TYPE_HOST		9
-#define IF_TYPE_MAX		10	/* Max number of IF_TYPE_* supported */
+enum if_type {
+	IF_TYPE_UNKNOWN = 0,
+	IF_TYPE_IDE,
+	IF_TYPE_SCSI,
+	IF_TYPE_ATAPI,
+	IF_TYPE_USB,
+	IF_TYPE_DOC,
+	IF_TYPE_MMC,
+	IF_TYPE_SD,
+	IF_TYPE_SATA,
+	IF_TYPE_HOST,
+
+	IF_TYPE_COUNT,			/* Number of interface types */
+};
 
 struct blk_desc {
-	int		if_type;	/* type of the interface */
+	enum if_type	if_type;	/* type of the interface */
 	int		dev;		/* device number */
 	unsigned char	part_type;	/* partition type */
 	unsigned char	target;		/* target SCSI ID */