mwifiex: pcie: extract wifi part from combo firmware during function level reset

A separate wifi-only firmware was download during pcie function level
reset. It is in fact the tail part of wifi/bt combo firmware. Per
Brian's and Dmitry's suggestion, this patch extract the wifi part from
combo firmware.

After that, the mrvl/pcie8997_wlan_v4.bin image in linux-firmware repo
is redundant (though I guess we keep it around to support older
kernels).

Signed-off-by: Xinming Hu <huxm@marvell.com>
Signed-off-by: Ganapathi Bhat <gbhat@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>