ARM: dove: convert serial DT nodes to clocks property

of_serial now has support for using clocks property and we have
a DT clock provider. This patch replaces the hard coded clock-frequency
property with a clocks phandle to tclk.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>