am5729-beagleboneai.dts: mailbox5/mailbox6 enabled in dra7-ipu-dsp-common.dtsi

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>

Author: RobertCNelson

src/arm/am5729-beagleboneai.dts

@@ -1034,14 +1034,6 @@
 	status = "okay";
 };
 
-&mailbox5 {
-	status = "okay";
-};
-
-&mailbox6 {
-	status = "okay";
-};
-
 &mailbox7 {
 	status = "okay";
 };