drm/vmwgfx: Stop using dev_private to store driver data.

Currently vmwgfx uses the dev_private opaque pointer in drm_device to store
driver data in vmw_private struct. Using dev_private is deprecated, and the
recommendation is to embed struct drm_device in the larger per-device
structure.

The vmwgfx driver already embeds struct drm_device in its struct
vmw_private, so switch to using that exclusively and stop using
dev_private.

Signed-off-by: Maaz Mombasawala <maaz.mombasawala@broadcom.com>
Reviewed-by: Zack Rusin <zack.rusin@broadcom.com>
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240502004033.107533-1-maaz.mombasawala@broadcom.com