MX53: Remove CONFIG_SYS_BOOTMAPSZ from mx53 config files.

commit ed59e587 (Remove device tree booting dependency on CONFIG_SYS_BOOTMAPSZ) made the
definition of CONFIG_SYS_BOOTMAPSZ unnecessary.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Jason Liu <jason.hui@linaro.org>