The scan APIs of 12xx and 18xx are totally different.
Use some common functions as much as possible (e.g.
for setting scan channels), but split scan.c into
chip-specific scan.c files, each implementing its
own scan mechanism.

(in other words - move most of the current wlcore's
scan.c into wl12xx, and implement a similar mechanism
in 18xx, according to the new api)

New wlcore ops are introduced in order to call the
chip-specific scan functions.

The template indices used for each scan (regular/scheduled)
are also different between the chips, so set the correct
indices used for each scan type after identifying the chip.
Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>