realtek: update platform support for 5.15

- fw_passed_dtb and others were replaced to get_fdt() function[1]
- __appended_dtb defined by asm/bootinfo.h[2]

[1]: https://www.spinics.net/lists/linux-mips/msg03332.html
[2]: https://www.spinics.net/lists/linux-mips/msg03332.html

Signed-off-by: INAGAKI Hiroshi <[email protected]>

target/linux/realtek/files-5.15/arch/mips/rtl838x/prom.c

@@ -25,7 +25,6 @@
 #include <mach-rtl83xx.h>
 
 extern char arcs_cmdline[];
-extern const char __appended_dtb;
 
 struct rtl83xx_soc_info soc_info;
 const void *fdt;

target/linux/realtek/files-5.15/arch/mips/rtl838x/setup.c

@@ -35,11 +35,8 @@ void __init plat_mem_setup(void)
 
 	set_io_port_base(KSEG1);
 
-	if (fw_passed_dtb) /* UHI interface */
-		dtb = (void *)fw_passed_dtb;
-	else if (&__dtb_start[0] != &__dtb_end[0])
-		dtb = (void *)__dtb_start;
-	else
+	dtb = get_fdt();
+	if (!dtb)
 		panic("no dtb found");
 
 	/*