dt-bindings: rtc: rtc-sh: convert bindings to json-schema

Convert Real Time Clock for Renesas SH and ARM SoCs bindings documentation
to json-schema.  Also name bindings documentation file according to the
compat string being documented.

Also correct syntax error in interrupts field in example.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Rob Herring <robh@kernel.org>