drm/nouveau/device: separate construction of pci/tegra devices

drivers/gpu/drm/nouveau/include/nvif/os.h

drivers/gpu/drm/nouveau/include/nvkm/core/client.h

drivers/gpu/drm/nouveau/include/nvkm/core/device.h

drivers/gpu/drm/nouveau/include/nvkm/core/pci.h

drivers/gpu/drm/nouveau/include/nvkm/core/tegra.h

drivers/gpu/drm/nouveau/nouveau_drm.c

drivers/gpu/drm/nouveau/nvkm/engine/device/Kbuild

drivers/gpu/drm/nouveau/nvkm/engine/device/base.c

drivers/gpu/drm/nouveau/nvkm/engine/device/pci.c

drivers/gpu/drm/nouveau/nvkm/engine/device/priv.h

drivers/gpu/drm/nouveau/nvkm/engine/device/tegra.c