dt-bindings: gpu: Add Imagination Technologies PowerVR/IMG GPU

Add the device tree binding documentation for the IMG AXE GPU used in
TI AM62 SoCs.

Co-developed-by: Frank Binns <frank.binns@imgtec.com>
Signed-off-by: Frank Binns <frank.binns@imgtec.com>
Signed-off-by: Sarah Walker <sarah.walker@imgtec.com>
Signed-off-by: Donald Robson <donald.robson@imgtec.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/deb0a4659423a3b8a74addee7178b6df7679575d.1700668843.git.donald.robson@imgtec.com


Signed-off-by: Maxime Ripard <mripard@kernel.org>