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/tqma6s_wru4_mmc_defconfig b/configs/tqma6s_wru4_mmc_defconfig
index df4c87e..c1be704 100644
--- a/configs/tqma6s_wru4_mmc_defconfig
+++ b/configs/tqma6s_wru4_mmc_defconfig
@@ -65,4 +65,5 @@
 CONFIG_USB_STORAGE=y
 CONFIG_USB_HOST_ETHER=y
 CONFIG_USB_ETHER_SMSC95XX=y
+CONFIG_IMX_WATCHDOG=y
 CONFIG_OF_LIBFDT=y