wlcore: ifdef CONFIG_OF-dependant functions

some of_* functions are defined only if CONFIG_OF
is defined. make the relevant block dependant
on it.

make sure to handle invalid pdata now, as it might
not get overriden if CONFIG_OF is not defined.

Signed-off-by: Eyal Reizer <eyalr@ti.com>
Signed-off-by: Eliad Peller <eliad@wizery.com>