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/warp_defconfig b/configs/warp_defconfig
index 6a9c91e..63eee27 100644
--- a/configs/warp_defconfig
+++ b/configs/warp_defconfig
@@ -37,4 +37,5 @@
 CONFIG_USB_GADGET_PRODUCT_NUM=0xa4a5
 CONFIG_CI_UDC=y
 CONFIG_USB_GADGET_DOWNLOAD=y
+CONFIG_IMX_WATCHDOG=y
 CONFIG_OF_LIBFDT=y