[MTD] Restore MTD_ROM and MTD_RAM types

Let's not attempt the abolition of mtd->type until/unless it's properly
thought through. And certainly, let's not do it by halves.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

include/mtd/mtd-abi.h

@@ -24,10 +24,11 @@ struct mtd_oob_buf {
 };
 
 #define MTD_ABSENT		0
+#define MTD_RAM			1
+#define MTD_ROM			2
 #define MTD_NORFLASH		3
 #define MTD_NANDFLASH		4
 #define MTD_DATAFLASH		6
-#define MTD_GENERIC_TYPE	7
 
 #define MTD_WRITEABLE		0x400	/* Device is writeable */
 #define MTD_BIT_WRITEABLE	0x800	/* Single bits can be flipped */