Setup extra MIMC200 chip selects

Added code to setup the extra Flash and FRAM chip selects as used on the
MIMC200 board.

V2 moves the init code from the common "cpu.c" file into the board specific
setup file.

Signed-off-by: Mark Jackson <mpfj@mimc.co.uk>
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>