brcm80211: smac: use DMA-API calls for descriptor allocations

Using BCMA hides the specifics about the host interface. The
driver is now using the DMA-API to do dma related calls. BCMA
provides the device object to use in the DMA-API calls.

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