Move FCH header to a location accessible by all archs

A new header fch.h was created to store registers used by different AMD
drivers.  This header was included by i2c-piix4 in
commit 624b0d5696 ("i2c: piix4, x86/platform: Move the SB800 PIIX4 FCH
definitions to <asm/amd/fch.h>"). To prevent compile failures on non-x86
archs i2c-piix4 was set to only compile on x86 by commit 7e173eb82a
("i2c: piix4: Make CONFIG_I2C_PIIX4 dependent on CONFIG_X86").
This was not a good decision because loongarch and mips both actually
support i2c-piix4 and set it enabled in the defconfig.

Move the header to a location accessible by all architectures.

Fixes: 624b0d5696 ("i2c: piix4, x86/platform: Move the SB800 PIIX4 FCH definitions to <asm/amd/fch.h>")
Suggested-by: Hans de Goede <hansg@kernel.org>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Hans de Goede <hansg@kernel.org>
Link: https://lore.kernel.org/r/20250610205817.3912944-1-superm1@kernel.org
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

arch/x86/kernel/cpu/amd.c

@@ -9,7 +9,7 @@
 #include <linux/sched/clock.h>
 #include <linux/random.h>
 #include <linux/topology.h>
-#include <asm/amd/fch.h>
+#include <linux/platform_data/x86/amd-fch.h>
 #include <asm/processor.h>
 #include <asm/apic.h>
 #include <asm/cacheinfo.h>

drivers/i2c/busses/i2c-piix4.c

@@ -34,7 +34,7 @@
 #include <linux/dmi.h>
 #include <linux/acpi.h>
 #include <linux/io.h>
-#include <asm/amd/fch.h>
+#include <linux/platform_data/x86/amd-fch.h>
 
 #include "i2c-piix4.h"
 

drivers/platform/x86/amd/pmc/pmc-quirks.c

@@ -11,7 +11,7 @@
 #include <linux/dmi.h>
 #include <linux/io.h>
 #include <linux/ioport.h>
-#include <asm/amd/fch.h>
+#include <linux/platform_data/x86/amd-fch.h>
 
 #include "pmc.h"