p54pci: convert driver to use asynchronous firmware loading

Drivers that load firmware from their probe routine have problems with the
latest versions of udev as they get timeouts while waiting for user
space to start. The problem is fixed by using request_firmware_nowait()
and delaying the start of mac80211 until the firmware is loaded.

To prevent the possibility of the driver being unloaded while the firmware
loading callback is still active, a completion queue entry is used.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>