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/aristainetos2b_defconfig b/configs/aristainetos2b_defconfig
index 6641382..95c30632 100644
--- a/configs/aristainetos2b_defconfig
+++ b/configs/aristainetos2b_defconfig
@@ -50,4 +50,5 @@
 CONFIG_USB_STORAGE=y
 CONFIG_VIDEO=y
 # CONFIG_VIDEO_SW_CURSOR is not set
+CONFIG_IMX_WATCHDOG=y
 CONFIG_OF_LIBFDT=y