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/display5_defconfig b/configs/display5_defconfig
index 697138e..ab5ec59 100644
--- a/configs/display5_defconfig
+++ b/configs/display5_defconfig
@@ -75,3 +75,4 @@
 CONFIG_MXC_UART=y
 CONFIG_SPI=y
 CONFIG_MXC_SPI=y
+CONFIG_IMX_WATCHDOG=y