ARM: dts: mmp*: Make the serial ports compatible with xscale-uart

XScale serial port driver is perfectly capable of supporting this hardware. A
separate compatible string is probably a historical mess.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200320174107.29406-7-lkundrak@v3.sk


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>