staging: brcm80211: Remove abstractions for pci_(un)map_single

The driver had abstracted DMA mapping functions. As abstraction
is not required for the linux driver, these have been removed
and replaced by native linux functions.

Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>