configs: mediatek: do not autostart the watchdog on the Genio EVKs

U-Boot autostarts the SoC watchdog (CONFIG_WATCHDOG_AUTOSTART default
y) and services it from its main loop, but nothing services it after
ExitBootServices()/bootm: an EFI-booted OS that does not take over the
watchdog in time is reset mid-boot at a wall-clock-dependent point.

The MediaTek toprgu can count at most ~16 seconds, once firmware stops
servicing it at the handoff, the OS has whatever is left of those 16
seconds.

On the Genio 700 EVK the generic Ubuntu 26.04 arm64 image is hard-reset
before its first boot reaches the login prompt: the mtk-wdt driver is
a module loaded from the rootfs and cannot win that race. Nothing tells
a generic OS that the watchdog is armed, so the failure is silent and,
from the user's side, indistinguishable from broken firmware.

Disable WATCHDOG_AUTOSTART for the Genio EVK boards (mt8365_evk
directly, mt8188.config for the Genio 510/700).

Signed-off-by: Carlo Caione <[email protected]>
Reviewed-by: Tom Rini <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: David Lechner <[email protected]>

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