dt-bindings: serial: fsl-lpuart: add i.MXRT1050 compatible

Add i.MXRT1050 documentation for compatible string.

Cc: Giulio Benetti <giulio.benetti@benettiengineering.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jesse Taube <Mr.Bossman075@gmail.com>
Link: https://lore.kernel.org/r/20211215220538.4180616-7-Mr.Bossman075@gmail.com


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