Resolving a multisampled depth texture into
a single sampled texture is supported on >= SM4.1
hw. It is possible some previous hw support it.

The ability was tested on radeonsi and nvc0.
Apparently is is also supported for radeon >= r700.

This patch adds the MULTISAMPLE_Z_RESOLVE cap and
add it to the drivers. It is advertised for drivers
for which it is sure the ability is supported.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Axel Davy <axel.davy@ens.fr>