drm/i915/psr: Remove PSR2 FIXME

Now we are checking sink capabilities when probing PSR DPCD register
and then dynamically checking in if new state is compatible with PSR
in, so this FIXME can be dropped.

Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190308000050.6226-1-jose.souza@intel.com