drm/nouveau: replace drm_device* with nouveau_drm* as dev drvdata

drm/nouveau: replace drm_device* with nouveau_drm* as dev drvdata

We almost always want to cast the pointer from dev_get_drvdata() to
'struct nouveau_drm *', so just directly store that pointer instead,
simplifying callers, and fixing some clumsy naming of dev/drm_dev
variables at the same time.

Signed-off-by: Ben Skeggs <bskeggs@nvidia.com>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240726043828.58966-4-bskeggs@nvidia.com