drivers: Enable FPGA driver build on SPL

Enable FPGA driver build for Arria 10 SPL because FPGA driver is
needed by Arria 10 SPL to configure and getting DDR up before
loading U-boot into DDR and booting from there.

Signed-off-by: Tien Fong Chee <tien.fong.chee@intel.com>
Reviewed-by: Ley Foon Tan <ley.foon.tan@intel.com>
Reviewed-by: Dinh Nguyen <dinguyen@kernel.org>