p2p: support frequency for GroupJoin/GroupCreation with config

The frequency support is done in framework and supplicant.
Revise document to indicate the frequency can be used for fast group
connection API.

Bug: 64695709
Test: CtsVerifier - WiFi Direct
Test: manual test
      * specify frequency for Group Owner.
      * The group is run at specified frequency.
      * specify frequency for Group Client.
      * only specified frequency is scanned.
Test: Unit test - atest frameworks/opt/net/wifi/tests/wifitests
Test: build - make docs

Change-Id: Iedfdbf268af0d125611a81886881cdaebf017058