wl12xx: move hardcoded hci_io_ds value into the conf struct

Instead of hardcoding the hci_io_ds configuration that we write to the
SDIO_IO_DS top registed, read it from the default configuration so
that it's easier to change for different platforms.

Reported-by: Ido Yariv <ido@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>