serial: fsl_linflexuart: Update compatible string

The "fsl,s32-linflexuart" compatible string is too generic. Make it SoC
specific.

Signed-off-by: Stefan-Gabriel Mirea <stefan-gabriel.mirea@nxp.com>
Link: https://lore.kernel.org/r/20190823191115.18490-4-stefan-gabriel.mirea@nxp.com


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