drm/i915: convert the IRQ initialization functions to intel_uncore

The IRQ initialization helpers are simple and self-contained. Continue
the transition started in the recent uncore rework to get us rid of
I915_READ/WRITE and the implicit dev_priv variables.

While the implicit dev_priv is removed from the IRQ initialization
helpers, we didn't get rid of them in the macro callers. Doing that
should be very simple now.

v2: Rebase on top of the new patches.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> (v1)
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190410235344.31199-5-paulo.r.zanoni@intel.com