ARM: dts: at91: sam9x60: move flexcom definitions

Move the flexcom definitions from board specific DTS file
to the SoC specific DTSI file for sam9x60ek.

[durai.manickamkr@microchip.com: Logical split-up of this patch and added
 missing UART5 compatibles]

Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
Signed-off-by: Hari Prasath Gujulan Elango <Hari.PrasathGE@microchip.com>
Signed-off-by: Durai Manickam KR <durai.manickamkr@microchip.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20230207110651.197268-3-durai.manickamkr@microchip.com