dt-bindings: rtc: Convert sa1100-rtc to json-schema

Convert the sa1100-rtc binding to DT schema format using json-schema.
While add that, add clocks and resets that are actually used.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lore.kernel.org/r/20200616223353.993567-5-lkundrak@v3.sk


Signed-off-by: Rob Herring <robh@kernel.org>