arm64: dts: imx8mm-kontron: Disable pull resistors for SD card signals on BL board

Some signals have external pullup resistors on the board and don't need
the internal ones to be enabled. Due to silicon errata ERR050080 let's
disable the internal pull resistors whererever possible and prevent
any unwanted behavior in case they wear out.

Fixes: 8668d8b2 ("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>