acpigen,soc/amd,cpu/intel: rework static DWORD for CPPC table

Some elements in the ACPI CPPC table allow static DWORDs. Instead of
using a fake register resource, use a tagged union with the two types
"register" and "DWORD" and respective macros for CPPC table entries.

Test: dumped SSDT before and after do not differ.

Change-Id: Ib853261b5c0ea87ae2424fed188f2d1872be9a06
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57886
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/cpu/intel/common/common.h

@@ -4,6 +4,7 @@
 #define _CPU_INTEL_COMMON_H
 
 #include <types.h>
+#include <acpi/acpigen.h>
 
 void set_vmx_and_lock(void);
 void set_feature_ctrl_vmx(void);