ARM: dts: stm32: keep uart4 behavior on stm32mp157c-ed1

DMA configuration is added to uart nodes in stm32mp15x device tree.
Delete uart4 DMA property in stm32mp157c-ed1 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>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>