drm/i915/guc: Support larger contexts on newer hardware

The GuC needs a copy of a golden context for implementing watchdog
resets (aka media resets). This context is larger on newer platforms.
So adjust the size being allocated/copied accordingly.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220728024225.2363663-6-John.C.Harrison@Intel.com