The user submission is basically a pointer to a command list and a
pointer to uniforms.  We copy those in to the kernel, validate and
relocate them, and store the result in a GPU BO which we queue for
execution.

v2: Drop support for NV shader recs (not necessary for GL), simplify
    vc4_use_bo(), improve bin flush/semaphore checks, use __u32 style
    types.
Signed-off-by: Eric Anholt <eric@anholt.net>