arm64: dts: imx8mm-kontron: Disable pullups for onboard UART signals on BL board

arm64: dts: imx8mm-kontron: Disable pullups for onboard UART signals on BL board

[ Upstream commit 162aadaa0df8217b0cc49d919dd00022fef65e78 ]

These signals are actively driven by the SoC or by the onboard
transceiver. There's no need to enable the internal pull resistors
and due to silicon errata ERR050080 let's disable the internal ones
to prevent any unwanted behavior in case they wear out.

Fixes: 8668d8b2e67f ("arm64: dts: Add the Kontron i.MX8M Mini SoMs and baseboards")
Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>