drm/vmwgfx: Cleanup the vmw bo usage in the cursor paths

Base mapped count is useless because the ttm unmap functions handle
null maps just fine so completely remove all the code related to it.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Reviewed-by: Maaz Mombasawala <mombasawalam@vmware.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230131033542.953249-6-zack@kde.org