soc: renesas: r8a77965-sysc: Remove non-existent A3IR power domain

The R-Car Gen3 HardWare Manual Errata for Rev. 0.80 (Feb 28, 2018)
removed the A3IR power domain on R-Car M3-N, as this SoC does not have
an Image Processing Unit (IMP-X5).

The definition in the DT bindings header cannot be removed yet, until
its (incorrect) user has been removed.

Fixes: a527709b ("soc: renesas: rcar-sysc: Add R-Car M3-N support")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>