We were using first page of kernel context render state for sharing data
with GuC. While it's justified by the fact that those pages are not used
(note, GuC still enforces this layout and refuses to work if we remove
the extra page in front), it's also confusing (why are we using this
particular page?). Let's allocate a separate object instead.

v2: Drop kernel_context from GuC suspend/resume action handlers (Michel)
Suggested-by: NDaniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: NMichał Winiarski <michal.winiarski@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Jeff McGee <jeff.mcgee@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: NDaniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171025200020.16636-4-michal.winiarski@intel.com