agp/intel: Move intel_fake_agp_sizes into #ifdef block

Move the intel_fake_agp_sizes array into the same #ifdef block as it is
used to avoid instantiation when not used, and so triggering a compiler
warning

drivers/char/agp/intel-gtt.c:335:42: warning: ‘intel_fake_agp_sizes’
defined but not used [-Wunused-const-variable=]

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170121182233.30852-1-chris@chris-wilson.co.uk
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>