layout: Add capacity field

Use it to keep track of the size of the `entries` array. An interim
solution until we have dynamic allocation.

Change-Id: Ib5f431bc0a72a79a53fa1376c3417942b19dd3a0
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/33516
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-by: Peter Marheine <pmarheine@chromium.org>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

ich_descriptors.c

@@ -1295,6 +1295,7 @@ int layout_from_ich_descriptors(struct ich_layout *const layout, const void *con
 		++j;
 	}
 	layout->base.entries = layout->entries;
+	layout->base.capacity = ARRAY_SIZE(layout->entries);
 	layout->base.num_entries = j;
 	return 0;
 }