fpga: Add Kconfig to fpga subsystem

Add missing Kconfig to fpga subsystem to be able
to add new options.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/drivers/Kconfig b/drivers/Kconfig
index 4f84469..4c555a0 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -20,6 +20,8 @@
 
 source "drivers/dma/Kconfig"
 
+source "drivers/fpga/Kconfig"
+
 source "drivers/gpio/Kconfig"
 
 source "drivers/hwmon/Kconfig"