nrf_wifi: system: Add raw TX aggregation support in host layer

Extend raw TX handling to match the updated nrf_wifi_raw_tx_pkt firmware structure. Add aggregation and num_frames fields to raw_tx_pkt_header so applications can configure aggregation per packet, populate per-frame pkt_length and frame_ddr_pointer arrays in the raw TX command, and coalesce multiple raw frames in the TX pending queue when aggregation is enabled.