Bluetooth: CMTP: Mark BT_CMTP as DEPRECATED

This marks BT_CMTP as DEPRECATED in preparation to get it removed.
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

net/bluetooth/cmtp/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
 config BT_CMTP
-	tristate "CMTP protocol support"
-	depends on BT_BREDR && ISDN_CAPI
+	tristate "CMTP protocol support (DEPRECATED)"
+	depends on BT_BREDR && ISDN_CAPI && DEPRECATED
 	help
 	  CMTP (CAPI Message Transport Protocol) is a transport layer
 	  for CAPI messages.  CMTP is required for the Bluetooth Common