drm/i915/skl: remove redundant DDI/IRQ reinitialization during PW1 enabling

We don't need to reinit DDI and IRQs during PW1 enabling any more, since
we don't toggle PW1 on-demand any more. We enable PW1 only as part of
the display core init sequence and after this we initialize both DDI and
IRQs later in the init sequence. So remove these init steps from the
power well code.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1446657859-9598-11-git-send-email-imre.deak@intel.com