mwifiex: add pcie usb/uart firmware download support

This patch adds support for downloading usb/uart firmware for
8997 chipset by reading the chip version.

Signed-off-by: Shengzhen Li <szli@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>