drm/xe: Add child contexts to the GuC context lookup

The CAT_ERROR message from the GuC provides the guc id of the context
that caused the problem, which can be a child context. We therefore
need to be able to match that id to the exec_queue that owns it, which
we do by adding child context to the context lookup.

While at it, fix the error path of the guc id allocation code to
correctly free the ids allocated for parallel queues.

v2: rebase on s/XE_WARN_ON/xe_assert

Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/590


Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>