dt-bindings: serial: 8250_omap: allow serdev subnodes

dt-bindings: serial: 8250_omap: allow serdev subnodes

additionalProperties: false
ignores the pattern matching for serdev objects in serial.yaml, causing
error messages when serdev subnodes like bluetooth or gnss devices are
defined. Using unevaluatedProperties instead is the correct way
if arbitrary children nodes can appear.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Link: https://lore.kernel.org/r/20211001211731.2923066-1-andreas@kemnade.info
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>