ARM: socfpga: Set default DTB address on A10

Set default DT blob address on A10 SoCDK, since this SoC uses OF
separate configuration. The 0xf0000 address is just below the text
base and still leaves enough room for the DT to grow.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <chin.liang.see@intel.com>
Cc: Dinh Nguyen <dinguyen@kernel.org>