mx7_common: Put early/late init configs into board file

CONFIG_BOARD_EARLY_INIT_F and CONFIG_BOARD_LATE_INIT should not be
placed into mx7_common because not all boards need these options.

Move them to the board file instead.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>