sifive: fu540: add ddr driver

Add driver for fu540 to support ddr initialization in SPL.
This driver is based on FSBL
(https://github.com/sifive/freedom-u540-c000-bootloader.git)

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/ram/sifive/Kconfig b/drivers/ram/sifive/Kconfig
new file mode 100644
index 0000000..6aca22a
--- /dev/null
+++ b/drivers/ram/sifive/Kconfig
@@ -0,0 +1,13 @@
+config RAM_SIFIVE
+	bool "Ram drivers support for SiFive SoCs"
+	depends on RAM && RISCV
+	default y
+	help
+	  This enables support for ram drivers of SiFive SoCs.
+
+config SIFIVE_FU540_DDR
+	bool "SiFive FU540 DDR driver"
+	depends on RAM_SIFIVE
+	default y if TARGET_SIFIVE_FU540
+	help
+	  This enables DDR support for the platforms based on SiFive FU540 SoC.