arch/x86: factor out and commonize HPET_BASE_ADDRESS definition

All x86 chipsets and SoCs have the HPET MMIO base address at 0xfed00000,
so define this once in arch/x86 and include this wherever needed. The
old AMD AGESA code in vendorcode that has its own definition is left
unchanged, but sb/amd/cimx/sb800/cfg.c is changed to use the new common
definition.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Ifc624051cc6c0f125fa154e826cfbeaf41b4de83
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62304
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>

src/southbridge/amd/cimx/sb800/cfg.c

@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#include <arch/hpet.h> /* Include this before OEM.h to have HPET_BASE_ADDRESS from arch/x86 */
 #include "SBPLATFORM.h"
 #include "cfg.h"
 #include <OEM.h>