soc/intel/alderlake: Allow channel 0 for memory-down

Fixes detection of the on-board RAM (Samsung K4AAG165WA-BCWE) on the
System76 Lemur Pro 11 (lemp11).

Change-Id: Ibe56c0f2b81d660303429cd2e21a7bb6cd433da5
Signed-off-by: Tim Crawford <tcrawford@system76.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/65567
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <inforichland@gmail.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Jeremy Soller <jeremy@system76.com>

src/soc/intel/alderlake/meminit.c

@@ -54,8 +54,8 @@ static const struct soc_mem_cfg soc_mem_cfg[] = {
 			 * configuration.
 			 */
 			.half_channel = BIT(0),
-			/* In mixed topologies, channel 1 is always memory-down. */
+			/* In mixed topologies, either channel 0 or 1 can be memory-down. */
-			.mixed_topo = BIT(1),
+			.mixed_topo = BIT(0) | BIT(1),
 		},
 	},
 	[MEM_TYPE_DDR5] = {