AMD Bettong: Enable S4 feature for Windows 7

PMIOxEE is for setting USB3 power rail. Set it to S0, otherwise
going into hibernation can not be wake up.

Change-Id: I692497bad24d745738d670897e725a568c1db114
Signed-off-by: Zheng Bao <zheng.bao@amd.com>
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: http://review.coreboot.org/11373
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)

src/arch/x86/acpi.c

@@ -1005,6 +1005,12 @@ int acpi_is_wakeup_s3(void)
 	return (acpi_slp_type == 3);
 }
 
+int acpi_is_wakeup_s4(void)
+{
+	acpi_handoff_wakeup();
+	return (acpi_slp_type == 4);
+}
+
 void acpi_fail_wakeup(void)
 {
 	if (acpi_slp_type == 3 || acpi_slp_type == 2)