Kconfig: Convert CONFIG_IMX_WATCHDOG to Kconfig

Move this option to Kconfig and tidy up the config file of eight
boards which use it.

Signed-off-by: Xiaoliang Yang <xiaoliang.yang_1@nxp.com>
diff --git a/configs/kp_imx6q_tpc_defconfig b/configs/kp_imx6q_tpc_defconfig
index 84ca1ce..5ebbe1d 100644
--- a/configs/kp_imx6q_tpc_defconfig
+++ b/configs/kp_imx6q_tpc_defconfig
@@ -40,4 +40,5 @@
 CONFIG_IMX_THERMAL=y
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y
+CONFIG_IMX_WATCHDOG=y
 CONFIG_OF_LIBFDT=y