FT: Allow CCMP-256 and GCMP-256 as group ciphers

FT: Allow CCMP-256 and GCMP-256 as group ciphers

The FT-specific check for valid group cipher in wpa_ft_gen_req_ies() was
not up-to-date with the current list of supported ciphers. Fix this by
using a generic function to determine validity of the cipher. In
practice, this adds support for using CCMP-256 and GCMP-256 as the group
cipher with FT.

Signed-off-by: Jouni Malinen <j@w1.fi>