davinci: DM355: add base SoC and board support

In addition, add board support for the DM355 Evaluation Module (EVM)
and the DM355 Leopard board.

Original DM355 EVM support done by Sandeep Paulraj, with significant
updates and improvements by David Brownell.  DM355 Leopord support
done by Koen Kooi.

Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
Signed-off-by: Koen Kooi <koen@beagleboard.org>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>