dt-bindings: serial: fsl-lpuart: Drop i.MX8QXP backwards compatibility

Drop the i.MX8QXP backwards compatibility with i.MX7ULP since they
differ from clocks handling point of view.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Link: https://lore.kernel.org/r/20220210201407.567860-1-abel.vesa@nxp.com


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