ARM: mach-mx5/board-mx53_loco: Remove unused UARTs

On mx53_loco only UART1 is used and its signals go to connector J16.

Remove UART2 and UART3 as they are not used on this board.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Richard Zhao <richard.zhao@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>