dt-bindings: clock: ast2600: Add FSI clock

Add a definition for the FSI clock.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240215220759.976998-2-eajames@linux.ibm.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>