brcmfmac: add broken scatter-gather DMA support

DMA engine of some old SDIO host controllers require block size alignment for
data length of each scatterlist item. This patch introduces an intermediate
buffer list to support this kind of platform. It decreases the throughput
because of an extra memcpy in critical data path. So don't turn this on unless
it's necessary.

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