arm, davinci: Add support for the Calimain board from OMICRON electronics

This patch adds support for the Calimain board from
OMICRON electronics GmbH. The board features a Texas Instruments AM1808
SoC, 128 MB DDR2 memory, and 64 MB NOR flash memory connected to CS2 and
CS3.

Signed-off-by: Christian Riesch <christian.riesch@omicron.at>