davinci: Move emac platform_data to SoC-specific files

Since most of the emac platform_data is really SoC specific
and not board specific, move it to the SoC-specific files.
Put a pointer to the platform_data in the soc_info structure
so the board-specific code can set some of the platform_data
if it needs to.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>