configs: socfpga: Add defconfig for Agilex and Stratix 10 with ATF support

Booting Agilex and Stratix 10 with ATF support.

SPL now loads ATF (BL31), U-Boot proper and DTB from FIT
image. The new boot flow with ATF support is as follow:

SPL -> ATF (BL31) -> U-Boot proper -> OS (Linux)

U-Boot proper now starts at 0x200000 (CONFIG_SYS_TEXT_BASE).
ATF will occupy the address range starting from 0x1000.

Signed-off-by: Chee Hong Ang <chee.hong.ang@intel.com>
Signed-off-by: Siew Chin Lim <elly.siew.chin.lim@intel.com>