ARM: dts: stm32: keep uart4 behavior on stm32mp157c-lxa-mc1

DMA configuration is added to uart nodes in stm32mp15x device tree.
Delete uart4 DMA property in stm32mp157c-lxa-mc1 board device tree to
keep console in irq mode, as DMA support for console has been removed
from the driver by commit e359b441 ("serial: stm32: fix threaded
interrupt handling").

Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>