dt-bindings: iio: hmc425a: add conditional GPIO array size constraints

ADRF5740 and HMC540S have a 4 bit parallel interface.
Update ctrl-gpios description and min/maxItems values depending on the
matched compatible to correctly reflect the hardware properties.

Fixes: 79f2ff64 ("dt-bindings: iio: hmc425a: add entry for ADRF5740 Attenuator")
Fixes: 20f87a9a

 ("dt-bindings: iio: hmc425a: add entry for HMC540S")
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Dumitru Ceclan <mitrutzceclan@gmail.com>
Link: https://lore.kernel.org/r/20240220153553.2432-3-mitrutzceclan@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>