brcmsmac: remove ai_chipcontrl_epa4331

ai_chipcontrl_epa4331 is not referenced by any method in brcmsmac and
the functionality is already in bcma_chipco_bcm4331_ext_pa_lines_ctl in
drivers/bcma/driver_chipcommon_pmu.c

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>