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.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>