linux-firmware: add Marvell SD8997 firmware image

WLAN (SDIO) firmware version: W16.68.1.p179
Bluetooth (SDIO) firmware version: W16.26.1.p179

Both WLAN and bluetooth are on SDIO interface.
The combo image can be downloaded either through WLAN or
Bluetooth.

Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Ganapathi Bhat <gbhat@marvell.com>