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/astro_mcf5373l_defconfig b/configs/astro_mcf5373l_defconfig
index 2302b1f..dc01724 100644
--- a/configs/astro_mcf5373l_defconfig
+++ b/configs/astro_mcf5373l_defconfig
@@ -19,4 +19,5 @@
 CONFIG_FPGA_ALTERA=y
 CONFIG_FPGA_CYCLON2=y
 CONFIG_FPGA_XILINX=y
+CONFIG_FPGA_SPARTAN3=y
 CONFIG_MTD_NOR_FLASH=y