Add on-demand paging capabilities reporting to the extended query device verb.

Yann Droneaud writes:

    Note: as offsetof() is used to retrieve the size of the lower chunk
    of the response, beware that it only works if the upper chunk
    is right after, without any implicit padding. And, as the size of
    the latter chunk is added to the base size, implicit padding at the
    end of the structure is not taken in account. Both point must be
    taken in account when extending the uverbs functionalities.
Signed-off-by: Haggai Eran <haggaie@mellanox.com>
Reviewed-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>