ARM: dts: kirkwood: remove clock-frequency properties from UART nodes

UART devices found on Kirkwood SoCs derive their baudrate from TCLK.
With proper clocks property in the SoCs serial node, boards do not
need to overwrite it anymore.

Remove the remaining clock-frequency property from all Kirkwood boards.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lkml.kernel.org/r/1398862602-29595-5-git-send-email-sebastian.hesselbarth@gmail.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>