feat(imx8ulp): enable the DDR frequency scaling support

Enable the DDR frequency scaling support on i.MX8ULP.
Normally, the freq_index define is as below:

 0: boot frequency;
 1: low frequency(PLL bypassed);
 2. high frequency(PLL ON).

Currently, DDR DFS only do frequency switching between
Low freq and high freq.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Ye Li <ye.li@nxp.com>
Change-Id: I3acd8bdf75e2dd6dff645b9f597dcfc0a756c428
diff --git a/plat/imx/imx8ulp/include/dram.h b/plat/imx/imx8ulp/include/dram.h
new file mode 100644
index 0000000..9ed8969
--- /dev/null
+++ b/plat/imx/imx8ulp/include/dram.h
@@ -0,0 +1,13 @@
+/*
+ * Copyright 2024 NXP
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef DRAM_H
+#define DRAM_H
+
+void dram_init(void);
+
+#endif /* DRAM_H */
+