spi: renesas,rspi: Add r8a7742 to the compatible list

Document RZ/G1H (R8A7742) SoC specific bindings. The R8A7742 qspi module
is identical to R-Car Gen2 family.

No driver change is needed due to the fallback compatible value
"renesas,qspi".

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200812150048.27721-2-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>