watchdog: geode: restore hard CS5535_MFGPT dependency

Wtihout CONFIG_CS5535_MFGPT, the driver does not link right:

drivers/watchdog/built-in.o: In function `geodewdt_probe':
geodewdt.c:(.init.text+0xca3): undefined reference to `cs5535_mfgpt_alloc_timer'
geodewdt.c:(.init.text+0xcd4): undefined reference to `cs5535_mfgpt_write'
geodewdt.c:(.init.text+0xcef): undefined reference to `cs5535_mfgpt_toggle_event'

This adds back the dependency on this base driver.

Fixes: da2a68b3 ("watchdog: Enable COMPILE_TEST where possible")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>