drm/i915: Move HAS_PSR definition to platform struct definition

[patch series] Moving all GPU features to the platform struct definition
allows for
	- standard place when adding new features from new platforms
	- possible to see supported features when dumping struct definition

Signed-off-by: Carlos Santa <carlos.santa@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>