kconfig: Convert FPGA_SOCFPGA configuration to Kconfig

This converts the following to Kconfig:
   CONFIG_FPGA_SOCFPGA

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>
diff --git a/configs/socfpga_socrates_defconfig b/configs/socfpga_socrates_defconfig
index 8bf6164..a26be88 100644
--- a/configs/socfpga_socrates_defconfig
+++ b/configs/socfpga_socrates_defconfig
@@ -42,6 +42,7 @@
 CONFIG_SPL_DM=y
 CONFIG_SPL_DM_SEQ_ALIAS=y
 CONFIG_DFU_MMC=y
+CONFIG_FPGA_SOCFPGA=y
 CONFIG_DM_GPIO=y
 CONFIG_DWAPB_GPIO=y
 CONFIG_SYS_I2C_DW=y