ENGR00220884 uart: quit the early uart console as late as possible

ENGR00220884 uart: quit the early uart console as late as possible

If we use the late_initcall(), then there is a time slot between
the exit of early uart console and the real console:

      -->late_initcall(mxc_early_uart_console_disable)
	......
      -->imx_startup()

In this time slot, the clock will be closed, so the log printed during
the time slot is buffered, this is why we can not see the NFS's log.

Change the late_initcall() to late_initcall_sync() which eliminates the
time slot.

Signed-off-by: Huang Shijie <b32955@freescale.com>