libertas: convert libertas driver to use an event/cmdresp queue

This patch (co-developed by Dan Williams and Holger Schurig) uses a kfifo
object for events and a swapping buffer scheme for the command response to
preserve the zero-copy semantics of the CF driver and keep memory usage low.
The main thread should only ever touch the buffer indexed by priv->resp_idx,
while the interface code is free to write to the second buffer, then swap
priv->resp_idx under the driver spinlock.  The firmware specs only permit
one in-flight command, so there will only ever be one command response to
process at a time.

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas/defs.h

@@ -177,8 +177,6 @@ static inline void lbs_deb_hex(unsigned int grp, const char *prompt, u8 *buf, in
 #define MRVDRV_CMD_UPLD_RDY		0x0008
 #define MRVDRV_CARDEVENT		0x0010
 
-#define SBI_EVENT_CAUSE_SHIFT		3
-
 /** TxPD status */
 
 /*	Station firmware use TxPD status field to report final Tx transmit