ARM: dts: am335x-nano: Fix GPIO settings for RTS/CTS pins on UART3 & 4

The NanoBone platform uses GPIO pins for RTS/CTS control.
The DTS still uses the hardware RTS/CTS pins so this needs fixing.

Signed-off-by: Mark Jackson <mpfj@newflow.co.uk>
Message-Id: <20221130140547.295859-2-mpfj@newflow.co.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>