google/parrot: Add System Board ID to fix ACPI warning

Add the System Board Hardware ID to fix the warning:

dsdt.aml     88:  Device (MB) {
Warning  3141 -           ^ Missing dependency
(Device object requires a _HID or _ADR in same scope)

Change-Id: I063580142ae8053fdc05e165c01e86b8b7cd5ca6
Signed-off-by: Martin Roth <gaumless@gmail.com>
Reviewed-on: http://review.coreboot.org/10668
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/mainboard/google/parrot/acpi/mainboard.asl

@@ -83,6 +83,8 @@ Scope (\_SB) {
 	}
 
 	Device (MB) {
+		Name(_HID, EisaId("PNP0C01")) // System Board
+
 		/* Lid open */
 		Method (LIDO) { /* Not needed on this board */ }
 		/* Lid closed */