Add support for MPI-350 the mini-pci Cisco Aironet card. This needs more

Add support for MPI-350 the mini-pci Cisco Aironet card.  This needs more
work.  The interface was gleaned from the Linux driver.  Currently only
one RX & one TX buffer are used.  Firmware support is not tested so for the
MPI-350 so it is disabled.  Signal cache and monitor mode are not supported
yet.  Signal cache is not supported since in encapsulation mode ethernet
frames are returned by the chip.  LAN monitor mode support will be added
shortly.  Thanks to Warner for the MPI-350 card he sent me.

Add support for RSSI map from PR kern/32880 which was incomplete.  Enhanced
with the ability to select the cache mode of raw, dbm or per-cent.

Clean up Signal/Noise/Quality structures and units with help from
Marco Molteni.

Change flash to use a malloc'ed buffer when needed.

PR:		kern/32880
Submitted by:	Douglas S. J. De Couto decouto@pdos.lcs.mit.edu,
		Marco Molteni
MFC:		3 weeks