ravb: Document binding for r8a7795 SoC

This patch updates the ravb binding to support the r8a7795 SoC by:
- Adding a compat string for the new hardware
- Adding 25 named interrupts to binding for the new SoC;
  older SoCs continue to use a single multiplexed interrupt

The example is also updated to reflect the r8a7795 as this is the
more complex case.

Based on work by Kazuya Mizuguchi and others.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>