drm/i915/guc: Update sizes of CTB buffers

Future GuC will require CTB buffers sizes to be multiple of 4K.
Make these changes now as this shouldn't impact us too much.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Cc: John Harrison <john.c.harrison@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210603230408.54856-2-matthew.brost@intel.com