soc/intel: drop Kconfig `PM_ACPI_TIMER_OPTIONAL`

Technically, it's not depending on the hardware but on the software
(OS/payload), if the PM Timer is optional. OSes with ACPI >= 5.0A
support disabling of the PM Timer, when the respective FADT flag is
unset. Thus, drop this guard.

For platforms without hardware PM Timer (Apollo Lake, Gemini Lake) the
Kconfig `USE_PM_ACPI_TIMER` depends on `!NO_PM_ACPI_TIMER`.

As of this change, new platforms must either implement code for
disabling the hardware PM timer or select `NO_PM_ACPI_TIMER` if no such
is present.

Change-Id: I973ad418ba43cbd80b023abf94d3548edc53a561
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58017
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Lance Zhao
diff --git a/src/soc/intel/common/block/acpi/acpi.c b/src/soc/intel/common/block/acpi/acpi.c
index af7212e..1601777 100644
--- a/src/soc/intel/common/block/acpi/acpi.c
+++ b/src/soc/intel/common/block/acpi/acpi.c
@@ -142,7 +142,7 @@
 			ACPI_FADT_SLEEP_BUTTON |
 			ACPI_FADT_SEALED_CASE | ACPI_FADT_S4_RTC_WAKE;
 
-	if (CONFIG(USE_PM_ACPI_TIMER) || !CONFIG(PM_ACPI_TIMER_OPTIONAL))
+	if (CONFIG(USE_PM_ACPI_TIMER))
 		fadt->flags |= ACPI_FADT_PLATFORM_CLOCK;
 
 	fadt->x_pm1a_evt_blk.space_id = ACPI_ADDRESS_SPACE_IO;