ARM: dts: at91: sama5d2: Specify the FIFO size for the Flexcom UART

The UART submodule in Flexcom has 32-byte Transmit and Receive FIFOs.
Tested uart7 on sama5d2-icp, which has both DMA and FIFO enabled.
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20200514050301.147442-8-tudor.ambarus@microchip.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

arch/arm/boot/dts/sama5d2.dtsi

@@ -701,6 +701,7 @@ AT91_XDMAC_DT_PERID(13))>,
 						 AT91_XDMAC_DT_PER_IF(1) |
 						 AT91_XDMAC_DT_PERID(14))>;
 					dma-names = "tx", "rx";
+					atmel,fifo-size = <32>;
 					status = "disabled";
 				};
 
@@ -879,6 +880,7 @@ AT91_XDMAC_DT_PERID(15))>,
 						 AT91_XDMAC_DT_PER_IF(1) |
 						 AT91_XDMAC_DT_PERID(16))>;
 					dma-names = "tx", "rx";
+					atmel,fifo-size = <32>;
 					status = "disabled";
 				};
 			};