ARM: dts: ti: omap: am335x-regor: Fix RS485 settings

ARM: dts: ti: omap: am335x-regor: Fix RS485 settings

RTS pin seems to have inverted behavior on am335x, other than expected
with default "rs485-rts-active-high" (instead of low on idle, high on send,
it is the opposite). Transceiver datasheet also suggests a pulldown.
Add includes to pin definitions that are used.

Signed-off-by: Steffen Hemer <s.hemer@phytec.de>
Signed-off-by: Dominik Haller <d.haller@phytec.de>
Link: https://lore.kernel.org/r/20240730092353.10209-1-d.haller@phytec.de
Signed-off-by: Kevin Hilman <khilman@baylibre.com>