blackfin: bf60x: Port blackfin core architecture code to boot on bf60x.

Set up clocks, DDR controller, Nor flash controller, reboot,
serial port. Add new SPI boot modes.

Signed-off-by: Bob Liu <lliubbo@gmail.com>
Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Sonic Zhang <sonic.adi@gmail.com>