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/configs/r7780mp_defconfig b/configs/r7780mp_defconfig
index 44bf3a7..ed89aa9 100644
--- a/configs/r7780mp_defconfig
+++ b/configs/r7780mp_defconfig
@@ -26,7 +26,7 @@
 # CONFIG_CMD_SOURCE is not set
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_PING=y
-# CONFIG_CMD_MISC is not set
+# CONFIG_CMD_SLEEP is not set
 CONFIG_CMD_EXT2=y
 CONFIG_DOS_PARTITION=y
 CONFIG_ENV_OVERWRITE=y