gpu: nova-core: gsp: support large RPCs via continuation record

gpu: nova-core: gsp: support large RPCs via continuation record

Splits large RPCs if necessary and sends the remaining parts using
continuation records. RPCs that do not need continuation records
continue to write directly into the command buffer. Ones that do write
into a staging buffer first, so there is one copy.

Continuation record for receive is not necessary to support at the
moment because those replies do not need to be read and are currently
drained by retrying `receive_msg` on `ERANGE`.

Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
Link: https://patch.msgid.link/20260306-cmdq-continuation-v6-8-cc7b629200ee@nvidia.com
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>