arch-x86: Assign thread context id to APIC id

This change tries to enable a unique APIC id for a single thread
to enable smt support for x86

Change-Id: I3e7034b358623577c5ad4be3e51f08e48291ce49
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/35837
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/x86/interrupts.cc

@@ -317,7 +317,8 @@ X86ISA::Interrupts::setThreadContext(ThreadContext *_tc)
 
     BaseInterrupts::setThreadContext(_tc);
 
-    initialApicId = tc->cpuId();
+    // Update APIC ID to consider SMT threads
+    initialApicId = tc->contextId();
     regs[APIC_ID] = (initialApicId << 24);
     pioAddr = x86LocalAPICAddress(initialApicId, 0);
 }