wl18xx: add some boot operations and hw-specific configurations

Implement the boot operation.  Add a wl18xx-specific configuration
structure (namely to configure the mac and phy parameters).

The default hw configuration matches the DVP board.

Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Arik Nemtsov <arik@wizery.com>