x86/tdx: Annotate a noreturn function

objdump complains:

  vmlinux.o: warning: objtool: __tdx_hypercall()+0x74: unreachable instruction

because __tdx_hypercall_failed() won't return but panic the guest.
Annotate that that is ok and desired.

Fixes: eb94f1b6 ("x86/tdx: Add __tdx_module_call() and __tdx_hypercall() helper functions")
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220420115025.5448-1-bp@alien8.de

arch/x86/coco/tdx/tdcall.S

@@ -200,5 +200,6 @@ SYM_FUNC_START(__tdx_hypercall)
 .Lpanic:
 	call __tdx_hypercall_failed
 	/* __tdx_hypercall_failed never returns */
+	REACHABLE
 	jmp .Lpanic
 SYM_FUNC_END(__tdx_hypercall)