soc/intel/cannonlake: Enable wake from USB in S4

The xHCI controller supports waking the system from S1-S4.
Thus specify that the deepest sleep state is S4 in _PRW.

Tested on Prodrive/hermes. The board now wakes from S4 as well by
pressing a key on the USB keyboard.

Change-Id: I0bb266e70ee6b4eb8922671b7d0078db0d29a1da
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49224
Reviewed-by: Christian Walter <christian.walter@9elements.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/soc/intel/cannonlake/acpi/xhci.asl b/src/soc/intel/cannonlake/acpi/xhci.asl
index 7d89665..50c0cb8 100644
--- a/src/soc/intel/cannonlake/acpi/xhci.asl
+++ b/src/soc/intel/cannonlake/acpi/xhci.asl
@@ -67,7 +67,7 @@
 {
 	Name (_ADR, 0x00140000)
 
-	Name (_PRW, Package () { GPE0_PME_B0, 3 })
+	Name (_PRW, Package () { GPE0_PME_B0, 4 })
 
 	Method (_DSW, 3)
 	{
@@ -79,6 +79,9 @@
 	Name (_S0W, 3)	/* D3 can wake device in S0 */
 	Name (_S3W, 3)	/* D3 can wake system from S3 */
 
+	Name (_S4D, 3)	/* D3 supported in S4 */
+	Name (_S4W, 3)	/* D3 can wake system from S4 */
+
 	OperationRegion (XPRT, PCI_Config, 0x00, 0x100)
 	Field (XPRT, AnyAcc, NoLock, Preserve)
 	{