drm/v3d: Add a CPU job submission

Create a new type of job, a CPU job. A CPU job is a type of job that
performs operations that requires CPU intervention. The overall idea is
to use user extensions to enable different types of CPU job, allowing the
CPU job to perform different operations according to the type of user
extension. The user extension ID identify the type of CPU job that must
be dealt.

Having a CPU job is interesting for synchronization purposes as a CPU
job has a queue like any other V3D job and can be synchoronized by the
multisync extension.

Signed-off-by: Melissa Wen <mwen@igalia.com>
Co-developed-by: Maíra Canal <mcanal@igalia.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231130164420.932823-9-mcanal@igalia.com