watchdog: iTCO: fix link error

When the MFD driver is a loadable module, the watchdog driver fails
to get linked into the kernel:

drivers/watchdog/iTCO_wdt.o: In function `update_no_reboot_bit_pmc':
iTCO_wdt.c:(.text+0x54f): undefined reference to `intel_pmc_gcr_update'

The code is written to support operation without the MFD driver, so
add a Kconfig dependency that allows this, while disallowing the watchdog
to be built-in when the MFD driver is a module.

Fixes: 25f1ca31 ("platform/x86: intel_pmc_ipc: Convert to MFD")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/watchdog/Kconfig

@@ -1217,6 +1217,7 @@ config ITCO_WDT
 	depends on (X86 || IA64) && PCI
 	select WATCHDOG_CORE
 	depends on I2C || I2C=n
+	depends on MFD_INTEL_PMC_BXT || !MFD_INTEL_PMC_BXT
 	select LPC_ICH if !EXPERT
 	select I2C_I801 if !EXPERT && I2C
 	---help---