Add SoC and platform-specific data and init for DaVinci EMAC network
driver.
Signed-off-by: NKevin Hilman <khilman@deeprootsystems.com>

Rework DM644x code into SoC specific and board specific parts.
This is also to generalize the structure a bit so it's easier to add
support for new SoCs in the DaVinci family.
Signed-off-by: NKevin Hilman <khilman@deeprootsystems.com>