hp/pavilion_m6_1035dx: Fix IASL warning - Missing _HID object

- Add System board _HID object.
- Remove Kconfig default disabling IASL warnings as errors

Fixes warning:
dsdt.aml     64:  Device (MB) {
Warning  3141 -           ^ Missing dependency
(Device object requires a _HID or _ADR in same scope)

Change-Id: I4fa6ab2a6744d58ded8b0feb361e002d90e11474
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/12532
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/mainboard/hp/pavilion_m6_1035dx/Kconfig

@@ -65,8 +65,4 @@ config VGA_BIOS_ID
 	string
 	default "1002,9900"
 
-# TODO: Remove this when platform ASL is fixed
-config IASL_WARNINGS_ARE_ERRORS
-	def_bool n
-
 endif # BOARD_HP_PAVILION_M6_1035DX

src/mainboard/hp/pavilion_m6_1035dx/acpi/mainboard.asl

@@ -101,6 +101,8 @@ Scope (\_SB) {
 	}
 
 	Device (MB) {
+		Name(_HID, EisaId("PNP0C01")) // System Board
+
 		/* Lid open */
 		Method (LIDO) { /* Stub */ }
 		/* Lid closed */