Let the machine pass to the platform which clock is used by the uart.
Enable the clock and use clk_get_rate() to determine its rate.
Signed-off-by: NAndrew Lunn <andrew@lunn.ch>
Tested-by: NJamie Lentin <jm@lentin.co.uk>
Signed-off-by: NMike Turquette <mturquette@linaro.org>