drm/qxl: Do not pin buffer objects for vmap

Pin and vmap are distinct operations. Do not perform a pin as part
of the vmap call. This used to be necessary to keep the fbdev buffer
in place while it is being updated. Fbdev emulation has meanwhile
been fixed to lock the buffer correctly. Same for vunmap.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> # virtio-gpu
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240227113853.8464-14-tzimmermann@suse.de