p54: enable 2.4/5GHz spectrum by eeprom bits.

Badness at /home/proski/src/linux-2.6/net/mac80211/rx.c:2200
NIP: c02bc850 LR: c02ab268 CTR: 00000000
REGS: ef01fcc0 TRAP: 0700   Tainted: G        W  (2.6.27-wl)
MSR: 00029032 <EE,ME,IR,DR>  CR: 22004084  XER: 20000000
TASK = c1a58800[1778] 'p54pci' THREAD: ef01e000
[...]
NIP [c02bc850] __ieee80211_rx+0x17c/0x638
LR [c02ab268] ieee80211_tasklet_handler+0x104/0x120
Call Trace:
[ef01fd70] [c1a0c020] 0xc1a0c020 (unreliable)
[ef01fdb0] [c02ab268] ieee80211_tasklet_handler+0x104/0x120
[...]

the problem was that some older cards are mis-identified and didn't support
5GHz rates, while they have the right MAC & Synth chip.

This patch changes the way how p54 decides if it should enable 11a channels
or not.

Reported-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>