arm: socfpga: Convert Altera DDR SDRAM driver to use Kconfig

Convert Altera DDR SDRAM driver to use Kconfig method.
Enable ALTERA_SDRAM by default if it is on Gen5 target.
Arria 10 will have different driver.

Signed-off-by: Tien Fong Chee <tien.fong.chee@intel.com>
Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
diff --git a/drivers/Kconfig b/drivers/Kconfig
index 0e5d97d..3e6bbac 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -14,6 +14,8 @@
 
 source "drivers/crypto/Kconfig"
 
+source "drivers/ddr/Kconfig"
+
 source "drivers/demo/Kconfig"
 
 source "drivers/ddr/fsl/Kconfig"