ARM: dts: aspeed: wedge40: Update UART4 pin settings

Enable UART4's NRTS4 (A19) pin because the pin is used for RS485
software emulation.

Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
Link: https://lore.kernel.org/r/20200824182955.7988-3-rentao.bupt@gmail.com


Signed-off-by: Joel Stanley <joel@jms.id.au>