drm/i915/uc: Add function to define defaults for GuC/HuC enable

There is a module parameter for controlling what GuC/HuC features are
enabled. Setting to -1 means 'use the default'. However, the default
was not well defined, out of date and needs to be different across
platforms.

The default is now to disable both GuC and HuC on legacy platforms
where legacy means TGL/RKL and anything prior to Gen12. For new
platforms, the default is to load HuC but not enable GuC submission
as that has not landed yet.

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20210113220724.2484897-1-John.C.Harrison@Intel.com