wcn36xx: Improve feature caps exchange

* Response format is not in the canonical format.
  wcn36xx_smd_rsp_status_check cannot be used.

* Save the FW caps in wcn36xx struct for later use.

Signed-off-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>