ralink: Introduce fw_passed_dtb to arch/mips/ralink

This patch adds fw_passed_dtb to arch/mips/ralink to support
CONFIG_MIPS_RAW_APPENDED_DTB. Furthermore it adds a check that __dtb_start is
not the same address as __dtb_end.
Signed-off-by: Tobias Wolf <dev-NTEO@vplace.de>
Acked-by: John Crispin <john@phrozen.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14662/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/ralink/of.c

@@ -66,13 +66,21 @@ static int __init early_init_dt_find_memory(unsigned long node,
 
 void __init plat_mem_setup(void)
 {
+	void *dtb = NULL;
+
 	set_io_port_base(KSEG1);
 
 	/*
 	 * Load the builtin devicetree. This causes the chosen node to be
-	 * parsed resulting in our memory appearing
+	 * parsed resulting in our memory appearing. fw_passed_dtb is used
+	 * by CONFIG_MIPS_APPENDED_RAW_DTB as well.
 	 */
-	__dt_setup_arch(__dtb_start);
+	if (fw_passed_dtb)
+		dtb = (void *)fw_passed_dtb;
+	else if (__dtb_start != __dtb_end)
+		dtb = (void *)__dtb_start;
+
+	__dt_setup_arch(dtb);
 
 	of_scan_flat_dt(early_init_dt_find_memory, NULL);
 	if (memory_dtb)