cmd: Add a 'misc' command to access miscellaneous devices

Enable the command "misc" for accessing miscellaneous devices with
a MISC uclass driver. The command provides listing all MISC devices
as well as read and write functionalities via their drivers.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
diff --git a/cmd/Makefile b/cmd/Makefile
index c617474..da4e060 100644
--- a/cmd/Makefile
+++ b/cmd/Makefile
@@ -94,6 +94,7 @@
 obj-$(CONFIG_CMD_IO) += io.o
 obj-$(CONFIG_CMD_MFSL) += mfsl.o
 obj-$(CONFIG_CMD_MII) += mii.o
+obj-$(CONFIG_CMD_MISC) += misc.o
 obj-$(CONFIG_CMD_MDIO) += mdio.o
 obj-$(CONFIG_CMD_SLEEP) += sleep.o
 obj-$(CONFIG_CMD_MMC) += mmc.o