wil6210: support for "sparrow" hardware

New hardware release appears; it require some changes to properly support  it.
Introduce struct wil_board and "board" attribute in wil6210_priv;
keep hardware variant information in this structure.
fill it on probe(). Used in the reset flow.

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>