mwifiex: add PCIe8897 support

This patch adds PCIe8897 support to mwifiex.
In PCIe8897 PFU (pre-fetch unit) is enabled by default.
This patch adds support to accommodate this feaure as well.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: Nishant Sarmukadam <nishants@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: Frank Huang <frankh@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>