drm/i915: Remove variable length arrays from sseu debugfs printers

In order to enable -Wvla to prevent new variable length arrays being
used in i915.ko, we first must remove the existing VLA. Inside
i915_print_sseu_info(), VLA are used as the actual size of the sseu
depends on platform. Replace the VLA with the maximum required.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180313004055.25411-1-chris@chris-wilson.co.uk