serial: imx: remove the uart_console() check

The uart_console() check makes the clocks(clk_per and clk_ipg) opened
even when we close the console uart.

This patch enable/disable the clocks in imx_console_write(),
so we can keep the clocks closed when the console uart is closed.

Also remove the clock enable/disable oprations in the probe, we do not
need them any more.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>