ppc/kmeter1: remove unused define

CONFIG_CONS_INDEX is nowhere used for this board, we can drop it.

Signed-off-by: Holger Brunck <holger.brunck@ch.abb.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
CC: Priyanka Jain <priyanka.jain@nxp.com>
CC: Valentin Longchamp <valentin.longchamp@ch.abb.com>