xtensa: Move dram_init to xtfpga board file

This is a board level stuff.

Tested-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
diff --git a/board/cadence/xtfpga/xtfpga.c b/board/cadence/xtfpga/xtfpga.c
index 5110fed..6b92fe3 100644
--- a/board/cadence/xtfpga/xtfpga.c
+++ b/board/cadence/xtfpga/xtfpga.c
@@ -66,6 +66,11 @@
 #endif
 }
 
+int dram_init(void)
+{
+	return 0;
+}
+
 int board_postclk_init(void)
 {
 	gd->cpu_clk = get_board_sys_clk();