fpga: Added Kconfig support for FPGA_SPARTAN3

This patch added Kconfig support for FPGA_SPARTAN3 and migrates the
values over to the defconfigs.

Signed-off-by: Vipul Kumar <vipulk@xilinx.com>
Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
diff --git a/configs/x600_defconfig b/configs/x600_defconfig
index b63bf41..0aef5b6 100644
--- a/configs/x600_defconfig
+++ b/configs/x600_defconfig
@@ -40,6 +40,7 @@
 CONFIG_BOOTCOUNT_LIMIT=y
 CONFIG_SYS_BOOTCOUNT_ADDR=0xD2801FF8
 CONFIG_FPGA_XILINX=y
+CONFIG_FPGA_SPARTAN3=y
 CONFIG_SYS_I2C_DW=y
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y