dm: implement a Miscellaneous uclass

Implement a Miscellaneous uclass with generic read or
write operations. This class is used only for those
do not fit other more general classes.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/uclass-id.h b/include/dm/uclass-id.h
index 330ecd2..886a44c 100644
--- a/include/dm/uclass-id.h
+++ b/include/dm/uclass-id.h
@@ -39,6 +39,7 @@
 	UCLASS_LED,		/* Light-emitting diode (LED) */
 	UCLASS_LPC,		/* x86 'low pin count' interface */
 	UCLASS_MASS_STORAGE,	/* Mass storage device */
+	UCLASS_MISC,		/* Miscellaneous device */
 	UCLASS_MMC,		/* SD / MMC card or chip */
 	UCLASS_MOD_EXP,		/* RSA Mod Exp device */
 	UCLASS_PCH,		/* x86 platform controller hub */