mb/hp/snb_ivb_laptops: Do not set EC SLPT on S5

Linux kernel now uses S5 for reboot, which makes reboot fail if EC
SLPT bit is set.

Tested on HP EliteBook 2560p, reboot and S3 resume work after this
change.

Change-Id: I9b3ea737f85cc4045714263657bcdaac08f3a20d
Signed-off-by: Iru Cai <mytbk920423@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52089
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/mainboard/hp/snb_ivb_laptops/acpi/platform.asl

@@ -10,5 +10,8 @@ Method(_WAK,1)
 
 Method(_PTS,1)
 {
-	\_SB.PCI0.LPCB.EC0.SLPT = Arg0
+	If (Arg0 != 5)
+	{
+		\_SB.PCI0.LPCB.EC0.SLPT = Arg0
+	}
 }