mwifiex: add support for SD8887 chipset

This patch adds SD8887 support to mwifiex.
SD8887 is Marvell's 1x1 11ac solution.

The corresponding firmware image file is located at:
"mrvl/sd8887_uapsta.bin"

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Frank Huang <frankh@marvell.com>
Signed-off-by: Nishant Sarmukadam <nishants@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>