ARM: davinci: da850evm: Enable SPL_OF_CONTROL without PLATDATA

With the memory mapping giving us some more avialable RAM, this
updates the da850-evm-u-boot.dtsi to include the serial port, SPI
and Flash nodes along with some dependent nodes in the SPL dtb.
This also removes the platform data initialization code for the
serial port and SPI Flash.

Signed-off-by: Adam Ford <aford173@gmail.com>