svga: fix persistent mapped surface update to constant buffer

svga: fix persistent mapped surface update to constant buffer

Currently when a buffer is mapped with the persistent bit set and is
later bound as a constant buffer, the updated buffer content is not
properly updated to the constant buffer surface as the constant buffer
surface is different from the original buffer surface. Doing
a buffer copy to sync the content of the constant buffer will fix
the problem, but the buffer copy can be costly.
To properly fix the issue, instead of creating a secondary surface
for the constant buffer, the original buffer surface will be accessed as
a raw buffer.

This fixes the rendering issue running yuzu deko_basic.nro

Reviewed-by: Martin Krastev <krastevm@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25381>