watchdog: tqmx86_wdt: Fix build error

If TQMX86_WDT is y and WATCHDOG_CORE is m, building fails:

drivers/watchdog/tqmx86_wdt.o: In function `tqmx86_wdt_probe':
tqmx86_wdt.c:(.text+0x46e): undefined reference to `watchdog_init_timeout'
tqmx86_wdt.c:(.text+0x4e0): undefined reference to `devm_watchdog_register_device'

Select WATCHDOG_CORE to fix this.
Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: e3c21e08 ("watchdog: tqmx86: Add watchdog driver for the IO controller")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20191206124259.25880-1-yuehaibing@huawei.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/Kconfig

@@ -1445,6 +1445,7 @@ config SMSC37B787_WDT
 config TQMX86_WDT
 	tristate "TQ-Systems TQMX86 Watchdog Timer"
 	depends on X86
+	select WATCHDOG_CORE
 	help
 	This is the driver for the hardware watchdog timer in the TQMX86 IO
 	controller found on some of their ComExpress Modules.