driver: wifi: siwx91x: Add single and multi-channel scan support

This commit introduces support for single and multi-channel Wi-Fi scans.
The device can now scan one specific channel or multiple specified
channels.

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>