mwifiex: remove USB8897 chipset support

We don't have any customer using this chipset via USB
interface. if both mwifiex_pcie and mwifiex_usb modules
are enabled by user, sometimes mwifiex_usb wins the race
even if user wants wlan interface to be on PCIe and
USB for bluetooth. This patch solves the problem.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Frank Huang <frankh@marvell.com>
Signed-off-by: Nishant Sarmukadam <nishants@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>