serial: imx: Remove unneeded registration message

There is no real value in displaying "Serial: IMX driver" in every boot.

The uart_register_driver() can fail and even so the "Serial: IMX driver" will
be displayed, which is not really helpful.

This is particularly annoying when booting multi_v7_defconfig kernel on a SoC
that is not a i.MX and even though this message gets displayed.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>