drm/i915/psr: Only lookup for enabled CRTCs when forcing a fastset

Forcing a specific CRTC to the eDP connector was causing the
intel_psr_fastset_force() to mark mode_chaged in the wrong and
disabled CRTC causing no update in the PSR state.

Looks like our internal state track do not clear output_types and
has_psr in the disabled CRTCs, not sure if this is the expected
behavior or not but in the mean time this fix the issue.

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190308000050.6226-2-jose.souza@intel.com