WFD: Add Wi-Fi Display support

WFD: Add Wi-Fi Display support

This commit adds control interface commands and internal storage of
Wi-Fi Display related configuration. In addition, WFD IE is now added
to various P2P frames, Probe Request/Response, and (Re)Association
Request/Response frames. WFD subelements from peers are stored in the
P2P peer table.

Following control interface commands are now available:
SET wifi_display <0/1>
GET wifi_display
WFD_SUBELEM_SET <subelem> [hexdump of length+body]
WFD_SUBELEM_GET <subelem>

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>