drm: nova-drm: add initial driver skeleton

Add the initial nova-drm driver skeleton.

nova-drm is connected to nova-core through the auxiliary bus and
implements the DRM parts of the nova driver stack.

For now, it implements the fundamental DRM abstractions, i.e. creates a
DRM device and registers it, exposing a three sample IOCTLs.

  DRM_IOCTL_NOVA_GETPARAM
    - provides the PCI bar size from the bar that maps the GPUs VRAM
      from nova-core

  DRM_IOCTL_NOVA_GEM_CREATE
    - creates a new dummy DRM GEM object and returns a handle

  DRM_IOCTL_NOVA_GEM_INFO
    - provides metadata for the DRM GEM object behind a given handle

I implemented a small userspace test suite [1] that utilizes this
interface.

Link: https://gitlab.freedesktop.org/dakr/drm-test

 [1]
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Dave Airlie <airlied@redhat.com>
Link: https://lore.kernel.org/r/20250424160452.8070-3-dakr@kernel.org


[ Kconfig: depend on DRM=y rather than just DRM. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>