IB/ipath: Lock and always use shadow copies of GPIO register

The new LED blinking interface adds more contention for the
unprotected GPIO pins that were already shared, though not commonly at
the same time.  We add locks to the accesses to these pins so that
Read-Modify-Write is now safe.  Some of these locks are added at
interrupt context, so we shadow the registers which drive and inspect
these pins to avoid the mmio read/writes.  This mitigates the effects
of the locks and hastens us through the interrupt.

Add locking and always use shadows for registers controlling GPIO pins
(ExtCtrl and GPIOout). The use of shadows implies doing less I/O,
which can make I2C operation too fast on some platforms. An explicit
udelay(1) in SCL manipulation fixes that.

Signed-off-by: Michael Albaugh <michael.albaugh@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>