boards: thingy52_nrf52832: disable unused regulators

Some regulators can't be used in practice due to the limitations of the
Zephyr init priorities system. To make use of regulators using SX1509B
GPIOs, we would need regulators to be initialized at different
priorities, something not possible because we have a fixed priority
(CONFIG_REGULATOR_FIXED_INIT_PRIORITY) for all instances.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>