fpga: dfl: allocate platform device after feature device data

fpga: dfl: allocate platform device after feature device data

Delay calling platform_device_alloc() from build_info_create_dev() to
feature_dev_register(), now that the feature device data contains all
necessary data to create the feature device. This completes the new
function feature_dev_register(), which will be reused in a subsequent
commit to fully recreate the feature device when assigning a port.

In the function feature_dev_unregister(), reset the device pointer in
the feature data to NULL to signal that the platform device has been
destroyed. This will substitute device_is_registered() in a subsequent
commit. Reset the device pointer of each sub feature for consistency.

Convert is_feature_dev_detected() to check whether binfo->type is not
DFL_ID_MAX for deciding whether a feature device was detected during
feature parsing, instead of checking binfo->feature_dev for non-NULL.

Signed-off-by: Peter Colberg <peter.colberg@intel.com>
Reviewed-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
Reviewed-by: Basheer Ahmed Muddebihal <basheer.ahmed.muddebihal@linux.intel.com>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/20241120011035.230574-16-peter.colberg@intel.com
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>