drm/i915/skl: init/uninit display core as part of the HW power domain state

We need to initialize the display core part early, before initializing
the rest of the display power state. This is also described in the bspec
termed "Display initialization sequence". Atm we run this sequence
during driver loading after power domain HW state initialization which
is too late and during runtime suspend/resume which is unneeded and can
interere with DMC functionality which handles HW resources toggled
by this init/uninit sequence automatically. The init sequence must be
run as the first step of HW power state initialization and during
system resume. The uninit sequence must be run during system suspend.

To address the above move the init sequence to the initial HW power
state setup and the uninit sequence to a new power domains suspend
function called during system suspend.

As part of the init sequence we also have to reprogram the DMC firmware
as it's lost across a system suspend/resume cycle.

After this change CD clock initialization during driver loading will
happen only later after other dependent HW/SW parts are initialized,
while during system resume it will get initialized as the last step of
the init sequence. This distinction can be removed by some refactoring
of platform independent parts. I left this refactoring out from this
series since I didn't want to change non-SKL parts. This is a TODO for
later.

v2:
- fix error path in i915_drm_suspend_late()
- don't try to re-program the DMC firmware if it failed to load

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/1447774433-20834-1-git-send-email-imre.deak@intel.com

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