soc/intel: Return ACPI_S4 as previous sleep state

pmc_prev_sleep_state() isn't handling the case where acpi_sleep_from_pm1()
returns ACPI_S4. Pass that value along so it can get set as a
prev_sleep_state. Without this, consumers see prev_sleep_state as 0
and always treat resume as a cold boot. With this, consumers can
correctly do behavior specific to S4 resume, like skipping the
disconnect IPC command to the PMC on Alderlake systems.

BUG=b:230031158
TEST=Resume from S4 on Primus4es

Signed-off-by: Evan Green <evgreen@chromium.org>
Change-Id: I3fb3dc428a749db80293e51a04a2096514a7b689
Reviewed-on: https://review.coreboot.org/c/coreboot/+/64002
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>

src/soc/intel/common/block/pmc/pmclib.c

@@ -399,6 +399,9 @@ static int pmc_prev_sleep_state(const struct chipset_power_state *ps)
 			if (CONFIG(HAVE_ACPI_RESUME))
 				prev_sleep_state = ACPI_S3;
 			break;
+		case ACPI_S4:
+			prev_sleep_state = ACPI_S4;
+			break;
 		case ACPI_S5:
 			prev_sleep_state = ACPI_S5;
 			break;