ARM: davinci: clean up platform support

With the board file support gone, and the platform using
DT only, a lot of the remaining code is no longer referenced
and can be removed.

Technically, the DT file only references DA850, but since that
is very similar to DA830, I'm leaving the latter.

Acked-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>