arm64: dts: ti: k3-am64: Only set UART baud for used ports

arm64: dts: ti: k3-am64: Only set UART baud for used ports

As the binding for "current-speed" states, this should only be used
when the baud rate of an attached device cannot be detected. This is
the case for our attached on-board USB-to-UART converter used for
early kernel console. For all other unconnected/disabled ports this
can be configured in userspace later, DT is not the place for device
configuration, especially when there are already standard ways to
set serial baud in userspace.

Remove setting baud for all disabled serial ports and move setting
it for the couple enabled ports down into the board files.

Signed-off-by: Andrew Davis <afd@ti.com>
Link: https://lore.kernel.org/r/20230601184933.358731-1-afd@ti.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>