soc/intel/xeon_sp/skx: Add missing includes

Commit 985d956 (soc/intel/xeon_sp/skx/: Clean up soc_util.c) removed
some indirect header inclusions, which resulted in a build failure.

Change-Id: I1ef9b416b52a6a1275d699708a805d4ba49baef0
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/46662
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/xeon_sp/skx/chip.c

@@ -7,6 +7,7 @@
 #include <soc/acpi.h>
 #include <soc/ramstage.h>
 #include <soc/soc_util.h>
+#include <soc/util.h>
 
 struct pci_resource {
 	struct device        *dev;

src/soc/intel/xeon_sp/skx/cpu.c

@@ -9,6 +9,7 @@
 #include <soc/msr.h>
 #include <soc/cpu.h>
 #include <soc/soc_util.h>
+#include <soc/util.h>
 #include <assert.h>
 #include "chip.h"