drm/i915: Run psr_setup unconditionally

Due to runtime pm and system s/r we need to restore hw state every
time we enable a pipe again. Hence trying to avoid that is just
pointless book-keeping which Rodrigo then tried to work around by
manually adding psr_setup calls to our resume code.

Much simpler to just remove code instead.

v2: Properly bail out of psr exit if psr isn't enabled. Spotted by
Rodrigo.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>