ARM: dts: AM33xx/AM43xx: Rename wkup_m3 sub-mailbox node

The OMAP sub-mailbox used to communicate with the Wakeup M3 remote
processor is currently named wkup_m3. This name can be confused with
the remote processor node. So, rename this to mbox-wkup-m3 to remove
the ambiguity and to also adhere to the sub-mailbox node name convention
being added in the OMAP Mailbox YAML binding.

Signed-off-by: Suman Anna <[e-mail]>
Signed-off-by: Tony Lindgren <[e-mail]>

arch/arm/boot/dts/am33xx-l4.dtsi

···
 				#mbox-cells = <1>;
 				ti,mbox-num-users = <4>;
 				ti,mbox-num-fifos = <8>;
-				mbox_wkupm3: wkup_m3 {
+				mbox_wkupm3: mbox-wkup-m3 {
 					ti,mbox-send-noirq;
 					ti,mbox-tx = <0 0 0>;
 					ti,mbox-rx = <0 0 3>;

arch/arm/boot/dts/am437x-l4.dtsi

···
 				#mbox-cells = <1>;
 				ti,mbox-num-users = <4>;
 				ti,mbox-num-fifos = <8>;
-				mbox_wkupm3: wkup_m3 {
+				mbox_wkupm3: mbox-wkup-m3 {
 					ti,mbox-send-noirq;
 					ti,mbox-tx = <0 0 0>;
 					ti,mbox-rx = <0 0 3>;