ddr: altera: Compile ALTERA SDRAM in SPL only

Compile ALTERA_SDRAM driver in SPL only.
Rename ALTERA_SDRAM to SPL_ALTERA_SDRAM.

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
diff --git a/drivers/ddr/altera/Kconfig b/drivers/ddr/altera/Kconfig
index 8f60b56..83c1ab5 100644
--- a/drivers/ddr/altera/Kconfig
+++ b/drivers/ddr/altera/Kconfig
@@ -1,5 +1,6 @@
-config ALTERA_SDRAM
-	bool "SoCFPGA DDR SDRAM driver"
+config SPL_ALTERA_SDRAM
+	bool "SoCFPGA DDR SDRAM driver in SPL"
+	depends on SPL
 	depends on TARGET_SOCFPGA_GEN5 || TARGET_SOCFPGA_ARRIA10
 	select RAM if TARGET_SOCFPGA_GEN5
 	select SPL_RAM if TARGET_SOCFPGA_GEN5
diff --git a/drivers/ddr/altera/Makefile b/drivers/ddr/altera/Makefile
index 3615b61..341ac0d 100644
--- a/drivers/ddr/altera/Makefile
+++ b/drivers/ddr/altera/Makefile
@@ -6,7 +6,7 @@
 # (C) Copyright 2010, Thomas Chou <thomas@wytron.com.tw>
 # Copyright (C) 2014 Altera Corporation <www.altera.com>
 
-ifdef CONFIG_ALTERA_SDRAM
+ifdef CONFIG_$(SPL_)ALTERA_SDRAM
 obj-$(CONFIG_TARGET_SOCFPGA_GEN5) += sdram_gen5.o sequencer.o
 obj-$(CONFIG_TARGET_SOCFPGA_ARRIA10) += sdram_arria10.o
 obj-$(CONFIG_TARGET_SOCFPGA_STRATIX10) += sdram_s10.o