dt-bindings: gpu: mali-valhall-csf: Add shader-present nvmem cell

dt-bindings: gpu: mali-valhall-csf: Add shader-present nvmem cell

On the MediaTek MT8196 SoC, the bitmask for which shader cores are
present and functional is not the one in the Mali GPU's registers, but
in an external efuse.

Add the nvmem cell properties to describe such a setup, and make them
required on MT8196.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Link: https://patch.msgid.link/20251220-mt8196-shader-present-v2-1-45b1ff1dfab0@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>