lynxpoint: export mem console pointer in ACPI

Instead of having an OS re-parse cbmem book-keeping records
for the cbmem allocator just to get the console buffer export
the pointer to the memory console directly in a field named 'CBMC'.
This field lives in the GNVS table.

Change-Id: Ief0c4da7b18df66feb9c816c9f4abdf5a72bd3a4
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/49764
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: http://review.coreboot.org/4149
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/mainboard/google/slippy/acpi_tables.c

@@ -92,6 +92,9 @@ static void acpi_create_gnvs(global_nvs_t *gnvs)
 	gnvs->chromeos.vbt2 = ACTIVE_ECFW_RO;
 #endif
 
+	/* Update the mem console pointer. */
+	gnvs->cbmc = (u32)cbmem_find(CBMEM_ID_CONSOLE);
+
 	acpi_update_thermal_table(gnvs);
 }