dt-bindings: clk: rename mpfs-clkcfg binding

The filename for a binding is supposed to match the first compatible,
but the mpfs-clkcfg file did not follow this policy. Rename it to match
so that when other mpfs clock bindings are added things make more sense.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220908143651.1252601-2-conor.dooley@microchip.com