staging: brcm80211: removed unused MIPS specific SDRAM swap window

Certain Mips based, big endian Broadcom products contain a memory window
for endianness swap purposes. However, this is too system specific for
this driver as there are more big endian platforms to support. Thus, this
'window' functionality is not to be used and can be removed.

The swap window would be a performance improvement and could be provided
with a dedicated mapping function in the platform specific code.

Tested on BCM63281.

Reviewed-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Tested-by: Jonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>