soc/intel/apl: Ensure CPU_CLUSTER linked_list bus exists

This fixes a NULL pointer deref introduced by 69cd729 (mb/*: Remove
lapic from devicetree).

Change-Id: I816fddfe3efe3c3aefe1b2ee28426dc1e1f3c962
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/72599
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
diff --git a/src/soc/intel/apollolake/cpu.c b/src/soc/intel/apollolake/cpu.c
index ec262f7..dba1923 100644
--- a/src/soc/intel/apollolake/cpu.c
+++ b/src/soc/intel/apollolake/cpu.c
@@ -273,6 +273,8 @@
 {
 	if (CONFIG(SOC_INTEL_COMMON_BLOCK_CPU_MPINIT))
 		return;
+	if (!dev->link_list)
+		add_more_links(dev, 1);
 	soc_init_cpus(dev->link_list);
 
 	/* Temporarily cache the memory-mapped boot media. */