Convert CONFIG_CMD_FPGAD to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_FPGAD

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/strider_con_dp_defconfig b/configs/strider_con_dp_defconfig
index 9524c9c..754db3d 100644
--- a/configs/strider_con_dp_defconfig
+++ b/configs/strider_con_dp_defconfig
@@ -17,6 +17,7 @@
 CONFIG_CMD_MEMTEST=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_I2C=y
+CONFIG_CMD_FPGAD=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y