mb: Set coreboot as DSDT's manufacturer model ID

Field 'OEMID' & "OEM Table ID" are related to DSDT table
not to mainboard.
So use macro to set them respectvely to "COREv4" and
"COREBOOT".

Change-Id: I060e07a730e721df4a86128ee89bfe168c69f31e
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/29790
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: David Guckian

src/mainboard/getac/p470/dsdt.asl

@@ -17,12 +17,13 @@
 #define ENABLE_TPM
 #undef  ENABLE_FDC	// There is no Floppy for this laptop
 
+#include <arch/acpi.h>
 DefinitionBlock(
 	"dsdt.aml",
 	"DSDT",
 	0x02,		// DSDT revision: ACPI v2.0 and up
-	"COREv4",	// OEM id
-	"COREBOOT",	// OEM table id
+	OEM_ID,
+	ACPI_TABLE_CREATOR,
 	0x20090419	// OEM revision
 )
 {