typhoon: repair firmware loading

The conversion to avoid using pci_alloc_consistent() broke the firmware
load process, as well as added an order-4 kmalloc and doubled the memory
usage of the firmware image. Go back to loading a page at a time.

Also, since the user can now give us utter garbage for firmware, do a
cursory validation so we don't try to load just anything.

Signed-off-by: David Dillow <dave@thedillows.org>
Signed-off-by: David S. Miller <davem@davemloft.net>