dt-bindings: gpu: add bindings for the ARM Mali Midgard GPU

dt-bindings: gpu: add bindings for the ARM Mali Midgard GPU

The ARM Mali Midgard GPU family is present in a number of SoCs
from many different vendors such as Samsung Exynos and Rockchip.

Import the device tree bindings documentation from the r16p0
release of the Mali Midgard GPU kernel driver:

  https://developer.arm.com/-/media/Files/downloads/mali-drivers/kernel/mali-midgard-gpu/TX011-SW-99002-r16p0-00rel0.tgz

Remove the copyright and GPL licence header as deemed not necessary.

Redesign the "compatible" property strings to list all the Mali
Midgard GPU types and add vendor specific ones.

Drop the "clock-names" property as the Mali Midgard GPU uses only one
clock (the driver now needs to call clk_get with NULL).

Convert the "interrupt-names" property values to lower-case: "job",
"mmu" and "gpu".

Replace the deprecated "operating-points" optional property with
"operating-points-v2".

Omit the following optional properties in this initial version as they
are only used in very specific cases:

  * snoop_enable_smc
  * snoop_disable_smc
  * jm_config
  * power_model
  * system-coherency
  * ipa-model

Update the example accordingly to reflect all these changes, based on
rk3288 mali-t760.

CC: John Reitan <john.reitan@arm.com>
Signed-off-by: Guillaume Tucker <guillaume.tucker@collabora.com>
Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>