[AVR32] Make STK1000 mux settings configurable

This adds some STK1002-specific config options covering the jumper settings,
so the kernel can automatically be configured to include the relevant devices.

One of them replaces the previous internal SW2_DEFAULT setting; SPI config
is affected by two of the jumpers; and a fourth one switches between LCD and
the second Ethernet connector.  (There's more that to be done.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>