ssb: add locking around gpio register accesses

The GPIOs are access through some registers in the chip common core or
over extif. We need locking around these GPIO accesses, all GPIOs are
accessed through the same registers and parallel writes will cause
problems.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Patchwork: http://patchwork.linux-mips.org/patch/4590
Acked-by: Florian Fainelli <florian@openwrt.org>

include/linux/ssb/ssb_driver_chipcommon.h

@@ -590,6 +590,7 @@ struct ssb_chipcommon {
 	u32 status;
 	/* Fast Powerup Delay constant */
 	u16 fast_pwrup_delay;
+	spinlock_t gpio_lock;
 	struct ssb_chipcommon_pmu pmu;
 };