dm: socfpga: Move driver model CONFIGs to Kconfig

Remove driver model CONFIGs from the board config headers and use Kconfig
instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/socfpga_socrates_defconfig b/configs/socfpga_socrates_defconfig
index 0f3896d..888bbb6 100644
--- a/configs/socfpga_socrates_defconfig
+++ b/configs/socfpga_socrates_defconfig
@@ -3,3 +3,6 @@
 +S:CONFIG_TARGET_SOCFPGA_CYCLONE5=y
 CONFIG_OF_CONTROL=y
 CONFIG_DEFAULT_DEVICE_TREE="socfpga_cyclone5_socrates"
+CONFIG_DM=y
+CONFIG_DM_SPI=y
+CONFIG_DM_SPI_FLASH=y