drm/nouveau: Fetch zcull info from device

drm/nouveau: Fetch zcull info from device

This information will be exposed to userspace in the following commit.

Add struct nvkm_gr_zcull_info, which serves as abstraction layer between
the corresponding uAPI (added in a subsequent patch) and the firmware
structure.

Extend the existing get_ctxbufs callback to also fill in zcull info.
ctxsw_size and ctxsw_align come from
NV2080_CTRL_CMD_INTERNAL_STATIC_KGR_GET_CONTEXT_BUFFERS_INFO, which is
already called by r570_gr_get_ctxbufs, while the rest of the zcull
info comes from
NV0080_CTRL_FIFO_GET_ENGINE_CONTEXT_PROPERTIES_ENGINE_ID_GRAPHICS_ZCULL.
Adding a separate callback for zcull info would require us to either:

1) Call GET_CONTEXT_BUFFERS_INFO twice, once for each callback. This
is a little slower and more verbose than calling it once.
or
2) Fill out zcull_info partially in r570_gr_get_ctxbufs and partially
in the new callback. Since we fill out only some of the info in each
we now need to handle edge cases where one function is called but not
the other as well as them being called in an arbitrary order.

Because of this, it's simplest to combine them in a single call
(get_ctxbufs_and_zcull_info), which avoids repeated rpc calls
to the gpu without the complexity of handling partially complete states.

Signed-off-by: Mel Henning <mhenning@darkrefraction.com>
Link: https://patch.msgid.link/20260219-zcull3-v3-1-dbe6a716f104@darkrefraction.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>