[Intel-gfx] Keeping Tvrtko busy

[Chris Wilson]

A continuation of the series under review to show the current path to
load balancing. After the HWSP timeline reworking, we have the removal
of global seqno, and then the patches to construct a virtual engine with
load balancing across the equivalent siblings. Wrt veng, the changes
since last time all centre around improving the uapi to remove more
implicit choices baked into the kernel and some bugfixes that came and
went thanks due to per-context seqno.
-Chris