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>

drivers/ddr/altera/Kconfig

@@ -0,0 +1,5 @@
+config ALTERA_SDRAM
+	bool "SoCFPGA DDR SDRAM driver"
+	depends on TARGET_SOCFPGA_GEN5
+	help
+	  Enable DDR SDRAM controller for the SoCFPGA devices.

drivers/ddr/altera/Makefile

@@ -8,4 +8,6 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-$(CONFIG_ALTERA_SDRAM) += sdram.o sequencer.o
+ifdef CONFIG_ALTERA_SDRAM
+obj-$(CONFIG_TARGET_SOCFPGA_GEN5) += sdram.o sequencer.o
+endif