brcmsmac: use sprom from bcma

bcma now provides all sprom attributes needed by brcmsmac and also
parses them from the pci sprom ant otp.

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>