driver: wifi: siwx91x: Add direct ssid scan support

This commit introduces support for direct SSID scans The feature allows
the device to send the probe requests and listen the beacon frame on the
specified SSID.

Co-authored-by: Arunmani Alagarsamy <arunmani.a@silabs.com>
Signed-off-by: Arunmani Alagarsamy <arunmani.a@silabs.com>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>