brcmfmac: use sdio functions to enable/disable F2

Instead of catching CCCR_IOEx register in F0 write access to
determine whether F2 state needs to change do it with direct
call to sdio_[enable/disable]_func().

Reviewed-by: Franky Lin <frankyl@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>