arm64: dts: renesas: r8a77961: Add GX6250 GPU node

arm64: dts: renesas: r8a77961: Add GX6250 GPU node

Describe Imagination Technologies PowerVR Rogue GX6250 BNVC 4.45.2.58
present in Renesas R-Car R8A77961 M3-W+ SoC.

Acked-by: Matt Coster <matt.coster@imgtec.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20251022033847.471106-3-marek.vasut+renesas@mailbox.org
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>