The Flexcom IP is part of the sama5d2 SoC. Move the flx0 node together
with its function definitions in sama5d2.dtsi. Boards will just fill
the pins and enable the desired functions.

There is a single functional change in this patch. With the move of the
flx0 uart5 definition in the SoC dtsi, the uart5 from
at91-sama5d27_wlsom1_ek.dts inherits the following optional property:
atmel,fifo-size = <32>;
This particular change was tested by Codrin.
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Tested-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Link: https://lore.kernel.org/r/20200514050301.147442-7-tudor.ambarus@microchip.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>