drm/i915/display: Check PSR parameter and flag only in state compute phase

Due to the debugfs flag, has_psr2 in CRTC state could have a different
value than psr.psr2_enabled and it was causing PSR2 subfeatures(DC3CO
and selective fetch) to be set to not a expected state.

So here only taking in consideration the parameter and debugfs flag
when computing PSR state, this way the CRTC state will also have
the correct state.

intel_psr_fastset_force() was already broken as
intel_psr_compute_config() was already only enabling PSR when
psr_global_enabled() and all other PSR requirements are met.
So some changes was required in this function, now it iterates over
all connectors, if it is a eDP connector and is active force a modeset
in the CRTC driving this connector, what will cause the new PSR state
to be set based on the debugfs flag.

v2:
- end connector iterator in error cases

Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201007195238.53955-2-jose.souza@intel.com