dt-bindings: mfd: atmel,at91sam9260: Convert to YAML schema

Changes during conversion:

Add a missing fallback `atmel,at91sam9x5-matrix` for
`microchip,sam9x60-matrix` which is not defined in the text binding.

Signed-off-by: Charan Pedumuru <charan.pedumuru@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20241218-matrix-v2-1-f3a8809ee5cd@microchip.com


Signed-off-by: Lee Jones <lee@kernel.org>