v3dv: implement double-buffer mode

v3dv: implement double-buffer mode

Double buffer mode splits the tile buffer size in half so we can
start processing the next tile while the current one is being
stored to memory. This mode is available only if MSAA is not enabled
and can, in theory, improve performance by reducing tile store
overhead, however, it comes at the cost of reducing the tile size,
which also causes some overhead of its own.

Testing shows that this helps some cases (i.e the Vulkan Quake
ports) but hurts others (i.e. Unreal Engine 4), so for the time
being we don't enable this by default but we allow to enable it
selectively by using V3D_DEBUG.

Reviewed-by: Juan A. Suarez <jasuarez@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14551>