davinci: add basic dm355/dm350/dm335 support

Add some basic declarations for DaVinci DM355/DM350/DM335 support,
keyed on CONFIG_SOC_DM355.  (DM35X isn't quite right because the
DM357 is very different; while the DM355 is like a DM355 without
the MPEG/JPEG coprocessor).

These have different peripherals than the DM6446, and some of
the peripherals are at different addresses.  Notably for U-Boot,
there's no EMAC, and the NAND controller address is different

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>