ath6kl: fix testmode when fw-2.bin or fw-3.bin is used

Testmode (TCMD and ART) was not enabled when fw-2.bin or fw-3.bin files
were available, fix that by fetching testmode file just after the
board file but before rest of the firmware files are fetched.

I also added testmode field to struct ath6kl and moved the module parameter
to core.c. Now all module parameters are grouped in one place.

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>