drm/i915: move platform_engine_mask and memory_regions to device info

The mock device creation was the only place that needed to modify
platform_engine_mask and memory_regions runtime. With mock_info in place
for mock devices, we can move them to device info.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/2083fb26468eef13defb9b70523f7f707fc93bad.1687878757.git.jani.nikula@intel.com