brcmfmac: simplify mapping of auth type

The 802.11 standard only has four valid auth type configurations of which
our firmware only supports two, ie. Open System and Shared Key. Simplify
the mapping falling back to automatic for other types specified by
user-space.

Reviewed-by: Arend Van Spriel <arend.vanspriel@broadcom.com>
Reviewed-by: Franky Lin <franky.lin@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Signed-off-by: Hante Meuleman <hante.meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>