ath6kl: testmode support

Add testmode support for running low level hardware tests. The testmode
is enabled by setting testmode module parameter to 1.

For now only a simple command passing is supported. More advanced
support will be implemented later.

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>