ACPI: Add helper fill_fadt_extended_pm_io()

Once platform code has filled in the (legacy) ACPI PM register
map, added function will fill in the extended entries in FADT.

TEST=samsung/lumpy and amd/mandolin FADT stays unchanged.

Change-Id: I90925fce35458cf5480bfefc7cdddebd41b42058
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74913
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@gmail.com>

src/include/acpi/acpi.h

@@ -1537,6 +1537,8 @@ void arch_fill_fadt(acpi_fadt_t *fadt);
 void soc_fill_fadt(acpi_fadt_t *fadt);
 void mainboard_fill_fadt(acpi_fadt_t *fadt);
 
+void fill_fadt_extended_pm_io(acpi_fadt_t *fadt);
+
 void acpi_fill_gnvs(void);
 void acpi_fill_cnvs(void);