wl18xx: translate and write the board type to SCR_PAD2

The firmware uses the SCR_PAD2 register to read the board type passed
from the driver.  The values don't match the ones used in the mac and
phy configuration, so we need to map them before writing.  This commit
adds a translation table that is used when writing the board type to
SCR_PAD2.

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