avr32: Solves problem with inverted MCI detect pin on Merisc board

Same patch as before, modified to use bool.

This patch solves the problem with the inverted mci detect pin on Merisc
boards.

Signed-off-by: Jonas Larsson <jonas.larsson@martinsson.se>
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>