DaVinci: move IDE platform device to its proper place

The IDE platform device is registered in three different places (2 board files
for DM644x and in dm646x.c for DM646x) while both the IDE base address and the
IDE IRQ are the same for both SoCs -- therefore,  the proper place for the IDE
platform seems to be in devices.c. Merge the IDE platform data and registration
code and create davinci_init_ide() in place of dm646x_init_ide()...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>