x86/of: Remove unused early_init_dt_add_memory_arch()

Recently objtool started complaining about dead code in the object files,
in particular

vmlinux.o: warning: objtool: early_init_dt_scan_memory+0x191: unreachable instruction

when CONFIG_OF=y.

Indeed, early_init_dt_scan() is not used on x86 and making it compile (with
help of CONFIG_OF) will abrupt the code flow since in the middle of it
there is a BUG() instruction.

Remove the pointless function.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20221124184824.9548-1-andriy.shevchenko@linux.intel.com

arch/x86/kernel/devicetree.c

@@ -31,11 +31,6 @@ char __initdata cmd_line[COMMAND_LINE_SIZE];
 
 int __initdata of_ioapic;
 
-void __init early_init_dt_add_memory_arch(u64 base, u64 size)
-{
-	BUG();
-}
-
 void __init add_dtb(u64 data)
 {
 	initial_dtb = data + offsetof(struct setup_data, data);