mwifiex: increase SDIO multiport aggregation buffer sizes

Currently Tx and Rx buffer sizes are 8K and 16K respectively for
all chipsets. We will change them to 32K for SD8897 and 16K for
older chipsets. SD8897 chipset has more SDIO data ports than
older chipsets.
This patch will help to improve throughput numbers.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>