linuxkpi: Support s2idle in pm_suspend_target_state

When going to s2idle, set Linux' pm_suspend_target_state to
PM_SUSPEND_TO_IDLE instead of setting PM_SUSPEND_MEM (for S3) in all
cases.

This is necessary because more recent versions of the amdgpu DRM drivers
have different paths for when entering s2idle & S0ix is supported than
S3.

Reviewed by:	bz
Approved by:	bz
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D51591

sys/compat/linuxkpi/common/src/linux_acpi.c

@@ -119,17 +119,27 @@ acpi_evaluate_dsm(ACPI_HANDLE ObjHandle, const guid_t *guid,
 }
 
 static void
-linux_handle_power_suspend_event(void *arg __unused,
-    enum power_stype stype __unused)
+linux_handle_power_suspend_event(void *arg __unused, enum power_stype stype)
 {
-	/*
-	 * Only support S3 for now.
-	 * acpi_sleep_event isn't always called so we use power_suspend_early
-	 * instead which means we don't know what state we're switching to.
-	 * TODO: Make acpi_sleep_event consistent
-	 */
-	linux_acpi_target_sleep_state = ACPI_STATE_S3;
-	pm_suspend_target_state = PM_SUSPEND_MEM;
+	switch (stype) {
+	case POWER_STYPE_SUSPEND_TO_IDLE:
+		/*
+		 * XXX: obiwac Not 100% sure this is correct, but
+		 * acpi_target_sleep_state does seem to be set to
+		 * ACPI_STATE_S3 during s2idle on Linux.
+		 */
+		linux_acpi_target_sleep_state = ACPI_STATE_S3;
+		pm_suspend_target_state = PM_SUSPEND_TO_IDLE;
+		break;
+	case POWER_STYPE_SUSPEND_TO_MEM:
+		linux_acpi_target_sleep_state = ACPI_STATE_S3;
+		pm_suspend_target_state = PM_SUSPEND_MEM;
+		break;
+	default:
+		printf("%s: sleep type %d not yet supported\n",
+		    __func__, stype);
+		break;
+	}
 }
 
 static void