dt-bindings: rtc: imxdi: Improve the bindings text

Improve the bindings text by doing the following changes:

- Remove the i.MX53 reference, as the RTC on i.MX53 is a different hardware
- Add 'clocks' to the list of required properties
- Explain that the optional security violation irq is the second entry
- Use the real unit address and irq numbers for i.MX25

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Acked-by: Juergen Borleis <jbe@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>