Add separate handling for adf4378 within the driver.

The main difference between adf4377 and adf4378 is that adf4378 has only
one output which is handled by only one gpio.
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Link: https://patch.msgid.link/20240729095047.25040-3-antoniu.miclaus@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>