cmd: Rename CMD_MISC to CMD_SLEEP

The "cmd/Kconfig" has a TODO description for CMD_MISC that it should
really be named as CMD_SLEEP. Change it in the whole source tree.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index a3166e4..cc7e931 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1708,8 +1708,7 @@
 	help
 	  Print bytes from the hardware random number generator.
 
-# TODO: rename to CMD_SLEEP
-config CMD_MISC
+config CMD_SLEEP
 	bool "sleep"
 	default y
 	help