ssb: remove rev from boardinfo

Previously the rev contained the revision read from the pci config
space and was used as board_rev in the wireless drivers. This is wrong
the board_rev is only fetched from the sprom accordingly to the open
source part of the Broadcom SDK and brcmsmac. This patch removes the
rev from the boardinfo structure and uses the board_rev attribute from
sprom instead. This attribute is filled by PCI, PCMCIA, SDIO and SoC
code.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Tested-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>