FABRIC-3.10.8 MC-1b: aarch64's second core online and parked

Cores from the DTB /cpus or, on QEMU (ACPI, no DTB), the MADT GICC
entries; the MADT lookup is now shared (hal/acpi.c) with amd64. PSCI
CPU_ON through the discovered conduit into ap_entry.S, which copies the
boot core's MMU/control state, sets TPIDR_EL1 and parks. Core 1 online
at EL1 with its own block; its vCPU thread 0.0% on the host. QEMU aarch64
-smp 2 -name debug-threads=on. 3-ISA acceptance clean.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

include/starkernel/smp.h

@@ -60,4 +60,8 @@ int arch_smp_start(BootInfo *boot_info, sk_percpu_t *pc, void *stack_top);
 /* One park step: interrupts stay masked; returns when the core wakes. */
 void arch_smp_park_once(void);
 
+/* Once `pc` is online: what the ISA can say about how it arrived (the
+ * exception level, the privilege mode), as a short phrase for its line. */
+const char *arch_smp_arrival(const sk_percpu_t *pc);
+
 #endif /* STARKERNEL_SMP_H */