dt-bindings: clock: mpfs-clkcfg: Add pic64gx compatibility

pic64gx has a clock controller compatible with mpfs-clkcfg. Don't permit
the deprecated configuration that was never supported for this SoC.

Signed-off-by: Pierre-Henry Moussay <pierre-henry.moussay@microchip.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>
Co-developed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20260113-glue-justifier-566ffab2ffd3@spud
Signed-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>