winsys/svga: fix display corruption after surface_init
When we initialize the buffer surface, do not map the existing storage
with DONTBLOCK, leave it as a synchronized map.
This patch also sets the surface rebind flag after it is bound to a
new buffer and sets the surface buffer pointer accordingly.
This fixes display corruption issue seen with running steam.
Reviewed-by: Neha Bhende <bhenden@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6415>