ARM: dts: AM33xx: Add ti,mbox-send-noirq to wkup_m3 mailbox

Add ti,mbox-send-noirq to wkup_m3 mailbox so that messages using
wkup_m3 mailbox are sent without triggering any further interrupts.
This is needed to achieve lower power numbers during CPU idle on
AM33xx.
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
[s-anna@ti.com: revise commit description]
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am33xx.dtsi

@@ -399,6 +399,7 @@ mailbox: mailbox@480C8000 {
 			ti,mbox-num-users = <4>;
 			ti,mbox-num-fifos = <8>;
 			mbox_wkupm3: wkup_m3 {
+				ti,mbox-send-noirq;
 				ti,mbox-tx = <0 0 0>;
 				ti,mbox-rx = <0 0 3>;
 			};