ARM: dts: stm32: don't use timers dmas on stm32mp157c-ed1

Spare dmas when using timer6 on stm32mp157c-ed1.
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32mp157c-ed1.dts

@@ -72,6 +72,9 @@ &rtc {
 
 &timers6 {
 	status = "okay";
+	/* spare dmas for other usage */
+	/delete-property/dmas;
+	/delete-property/dma-names;
 	timer@5 {
 		status = "okay";
 	};