dt-bindings: serial: 8250_omap: Add compatible for UART controller on AM64 SoC

AM64 uses a UART controller that is compatible with AM654 UART.
Introduce a specific compatible to help handle the differences if
necessary.

Reviewed-by: Nishanth Menon <nm@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20201029065318.2437-1-vigneshr@ti.com


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