dt-bindings: rtc: nxp,pcf8563: Convert to DT schema

Convert the Philips PCF8563/Epson RTC8564 binding to DT schema format.

Add 'interrupts' and 'wakeup-source' as this device has an interrupt
which was not documented, but in use. Add 'start-year' as well.

Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210526184839.2937899-3-robh@kernel.org