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/ge_bx50v3_defconfig b/configs/ge_bx50v3_defconfig
index 729377d..c907779 100644
--- a/configs/ge_bx50v3_defconfig
+++ b/configs/ge_bx50v3_defconfig
@@ -41,5 +41,6 @@
 CONFIG_MII=y
 CONFIG_SPI=y
 CONFIG_MXC_SPI=y
+CONFIG_IMX_WATCHDOG=y
 CONFIG_OF_LIBFDT=y
 # CONFIG_EFI_LOADER is not set