soc/intel/{skl,cnl}: replace PM ACPI timer dt option by Kconfig

Select `PM_ACPI_TIMER_OPTIONAL` to enable the new PM ACPI Kconfig and
set the FSP option for PM ACPI timer enablement from its value instead
of using the old devicetree option.

Also drop the obsolete devicetree option from soc code and from the
mainboards and add a corresponding Kconfig entry instead.

Change-Id: I10724ccf1647594404cec15c2349ab05b6c9714f
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45955
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/soc/intel/skylake/Kconfig b/src/soc/intel/skylake/Kconfig
index f71beae..ce46d06 100644
--- a/src/soc/intel/skylake/Kconfig
+++ b/src/soc/intel/skylake/Kconfig
@@ -42,6 +42,7 @@
 	select PLATFORM_USES_FSP2_0
 	select REG_SCRIPT
 	select SA_ENABLE_DPR
+	select PM_ACPI_TIMER_OPTIONAL
 	select PMC_GLOBAL_RESET_ENABLE_LOCK
 	select SOC_INTEL_COMMON
 	select SOC_INTEL_COMMON_ACPI_WAKE_SOURCE