b43legacy: Add driver load messages

This adds printk messages with basic information about the driver being loaded.
This information includes a summary of the compiled-in features, which
simplifies bug-reporting and debugging a lot.
Also a firmware ID is printed. This is a unique identifier blob for a specific
version of the firmware. This ID is attached to a specific version of the firmware
blob in b43-fwcutter (see fwcutter git).
This helps users to select the right firmware for their device.
This also makes it possible to use automated scripts to fetch and extract the right
firmware for the driver. (The script will grep the .ko for the "Firmware-ID: xxx" string.)
While the driver might still support other versions of the firmware for backward
compatibility, this will always print out the officially supported version, which
people _should_ use.

Signed-off-by: Stefano Brivio <stefano.brivio@polimi.it>
Signed-off-by: John W. Linville <linville@tuxdriver.com>