drm/panthor: Add support for Mali-Gx15 family of GPUs

Mali-Gx15 introduces a new GPU_FEATURES register that provides
information about GPU-wide supported features. The register value will
be passed on to userspace via gpu_info.

Additionally, Mali-Gx15 presents an 'Immortalis' naming variant
depending on the shader core count and presence of Ray Intersection
feature support.

This patch adds:
- support for correctly identifying the model names for Mali-Gx15 GPUs.
- arch 11.8 FW binary support

Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Karunika Choo <karunika.choo@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/20250807162633.3666310-5-karunika.choo@arm.com