cpu/cpu.h: Drop excessive includes

Change-Id: Ifeef04b68760522ce7f230a51f5df354e6da6607
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/17734
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/mainboard/google/slippy/acpi_tables.c

@@ -24,7 +24,6 @@
 #include <device/device.h>
 #include <device/pci.h>
 #include <device/pci_ids.h>
-#include <cpu/cpu.h>
 #include <cpu/x86/msr.h>
 #include <vendorcode/google/chromeos/gnvs.h>
 #include <ec/google/chromeec/ec.h>