ath9k : Display MAC/BB and RF version at startup (v2)

This patch decodes the MAC/BB version (for instance: AR5416) and the RF
part version (for instance: AR5133). It has been tested on AR5416/AR5133
which is a 2.4/5GHz 11n device. It also makes the differences between
AR5416 (PCI) and AR5418 (PCI Express). Both are named AR5416 in
the register definitions.

Signed-off-by: Benoit Papillault <benoit.papillault@free.fr>
Signed-off-by: John W. Linville <linville@tuxdriver.com>