tg3: Fix firmware loading

This patch modifies how the tg3 driver handles device firmware.

The patch starts by consolidating David Woodhouse's earlier patch under
the same name.  Specifically, the patch moves the request_firmware call
into a separate tg3_request_firmware() function and calls that function
from tg3_open() rather than tg3_init_one().

The patch then goes on to limit the number of devices that will make
request_firmware calls.  The original firmware patch unnecessarily
requested TSO firmware for devices that did not need it.  This patch
reduces the set of devices making TSO firmware patches to approximately
the following device set : 5703, 5704, and 5705.

Finally, the patch reduces the effects of a request_firmware() failure.
For those devices that are requesting TSO firmware, the driver will turn
off the TSO capability.  If TSO firmware becomes available at a later
time, the device can be closed and then opened again to reacquire the
TSO capability.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>