dt-bindings: arm: microchip,sam9x60-pit64b : convert to DT schema

dt-bindings: arm: microchip,sam9x60-pit64b : convert to DT schema

Convert Atmel Periodic interval timer of 64bit (PIT64b) binding to YAML
format.
Changes during conversion:
- Add missing compatible "microchip,sama7g5-pit64b" along with a fallback
compatible "microchip,sam9x60-pit64b".

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Akhila YS <akhilayalmati@gmail.com>
Link: https://lore.kernel.org/r/20260227-arm-microchip-v4-3-7e2ae1c5b5d6@gmail.com
[claudiu.beznea: alphanumerically sort the enum entries]
Signed-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>