da850evm: Use generic board and libfdt, fix size for SPI flash

da850evm: Use generic board and libfdt, fix size for SPI flash

Add defines to use CONFIG_SYS_GENERIC_BOARD and CONFIG_OF_LIBFDT.
Semi-separate to this: the size of the image for the da850evm has
increased to the point that the size in da850evm.h and the offset for
the environment in SPI flash no longer work.  They are modified to
account for the larger image size.

Signed-off-by: Peter Howard <phoward@gme.net.au>
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>