mt7620: fix missing kernel config symbol

mt7620: fix missing kernel config symbol

Fixes following missing kernel config symbol after adding GPIO watchdog:

  Software watchdog (SOFT_WATCHDOG) [M/n/y/?] m
  Watchdog device controlled through GPIO-line (GPIO_WATCHDOG) [Y/n/m/?] y
    Register the watchdog as early as possible (GPIO_WATCHDOG_ARCH_INITCALL) [N/y/?] (NEW)

Fixes: 1a97c03d864e ("rampis: feed zbt-we1026 external watchdog")
Signed-off-by: Petr Štetiar <ynezz@true.cz>
(cherry picked from commit fb2801b82c06878ae2ad20b8f95546c34ed3cdf4)

[adapted to config-5.4]

Signed-off-by: Federico Capoano <f.capoano@openwisp.io>