ARM: dts: am57xx-beagle-x15: Enable AFIFO use for McASP3

Since we switched to use eDMA we can now safely enable the FIFO in McASP.
This will reduce the chance of McASP level under/overflow.
Signed-off-by: NPeter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: NTony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am57xx-beagle-x15.dts

@@ -813,6 +813,8 @@
 	serial-dir = <	/* 0: INACTIVE, 1: TX, 2: RX */
 		1 2 0 0
 	>;
+	tx-num-evt = <32>;
+	rx-num-evt = <32>;
 };
 
 &mailbox5 {