mwifiex: remove support for old chipsets W0/W1

For SD8787 A0/A1 chipsets we use the default firmware image
file 'mrvl/sd8787_uapsta.bin'. So the chip rev id variable
is removed.

The global variable fw_name is moved to adapter structure
so that we can support a different interface, such as PCIe,
in future.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>