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/vexpress_ca15_tc2_defconfig b/configs/vexpress_ca15_tc2_defconfig
index 330b95c..e8e401b 100644
--- a/configs/vexpress_ca15_tc2_defconfig
+++ b/configs/vexpress_ca15_tc2_defconfig
@@ -19,7 +19,7 @@
 # CONFIG_CMD_ITEST is not set
 # CONFIG_CMD_SETEXPR is not set
 # CONFIG_CMD_NFS is not set
-# CONFIG_CMD_MISC is not set
+# CONFIG_CMD_SLEEP is not set
 CONFIG_CMD_UBI=y
 CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_FLASH=y