drm/xe/gsc: GSC FW load

The GSC FW must be copied in a 4MB stolen memory allocation, whose GGTT
address is then passed as a parameter to a dedicated load instruction
submitted via the GSC engine.

Since the GSC load is relatively slow (up to 250ms), we perform it
asynchronously via a worker. This requires us to make sure that the
worker has stopped before suspending/unloading.

Note that we can't yet use xe_migrate_copy for the copy because it
doesn't work with stolen memory right now, so we do a memcpy from the
CPU side instead.

v2: add comment about timeout value, fix GSC status checking
    before load (John)

Bspec: 65306, 65346
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>