linux-firmware: add Marvell 8887-A2 firmware image

WLAN (SDIO) firmware version: 15.68.7.p5
Bluetooth (SDIO) firmware version: 15.29.7.p5
The combo image can be downloaded through either WLAN or Bluetooth.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Frank Huang <frankh@marvell.com>