[platform][pc] when building with SMP, don't even attempt to bring up the local apic

Not exactly what we want but avoids the lapic code needing the per cpu
structures which aren't set up without SMP support.

Consider leaving the percpu structure in, just only support for cpu 0.

This fixes trying to boot the X86_LEGACY build on a machine with a local
apic.

platform/pc/interrupts.c

@@ -50,7 +50,10 @@ static struct int_vector int_table[INT_VECTORS];
 
 void platform_init_interrupts(void) {
     pic_init();
+
+#if WITH_SMP
     lapic_init();
+#endif
 
     // initialize all of the vectors
     for (int i = 0; i < INT_VECTORS; i++) {
@@ -227,9 +230,11 @@ static void io_apic_callback(const void *_entry, size_t entry_len, void *cookie)
 #endif
 
 void platform_init_interrupts_postvm(void) {
+#if WITH_SMP
     // Bring up the local apic on the first cpu
     // Doesn't need ACPI to detect its presence
     lapic_init_postvm();
+#endif
 
 #if WITH_LIB_ACPI_LITE
     // Now that we've scanned ACPI, try to initialize the ioapic(s)