brcmsmac: use bcma PCIe up and down functions

replace the calls to bcma_core_pci_extend_L1timer() by calls to the
newly introduced bcma_core_pci_ip() and bcma_core_pci_down()

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