drm/i915/display: Fix fastsets involving PSR

Commit 78b772e1

 ("drm/i915/display: Fill PSR state during hardware
configuration read out") is not allowing fastsets to happen when PSR
states changes but PSR is a feature that can be enabled and disabled
during fastsets.

So here moving the PSR pipe conf checks to a block that is only
executed when checking if HW state matches with requested state, not
during the phase where it checks if fastset is possible or not.

There still a state mismatch not allowing fastsets between states
turning off or on PSR because of crtc_state->infoframes.enable
BIT(DP_SDP_VSC) but at least for now it will allow a fastset between
PSR1 <-> PSR2, that is a case heavilly used by CI due to pipe CRC not
work with PSR2, but the remaning issue will be fixed in a future patch.

Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Fixes: 78b772e1

 ("drm/i915/display: Fill PSR state during hardware configuration read out")
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210514232247.144542-1-jose.souza@intel.com