drm/i915: unify gen6/gen8 rps irq enable/disable
drm/i915: unify gen6/gen8 rps irq enable/disable

The GEN6 and GEN8 versions differ only in the PM IIR and IER register
addresses and that on GEN8 we need to keep the
GEN8_PMINTR_REDIRECT_TO_NON_DISP PM interrupt unmasked. Abstract away
these 3 things in the GEN6 versions of the helpers and use them
everywhere.

No functional change.

Signed-off-by: Imre Deak <fbd5edba1988036c8923f0cca0cce6ac4811db29@intel.com>
Reviewed-by: Paulo Zanoni <cc0e04a2103c45cd195651d976f79813d0f66bdf@intel.com>
Signed-off-by: Daniel Vetter <c1b6782c4af8f0673da8923a0702a1832e5940f4@ffwll.ch>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs