drm/i915: refactor the IRQ init/reset macros

drm/i915: refactor the IRQ init/reset macros

The whole point of having macros here is for the token pasting
necessary to automatically have IMR, IIR and IER selected. We don't
really need or want all the inlining that happens as a consequence.
The good thing about the current code is that it works regardless of
the relative offsets between these registers (they change after gen4,
with the usual VLV/CHV exceptions).

One thing which we can do is to split the logic of what we do with
imr/ier/iir to functions separate from the macros that pick them.
That's what we do in this commit. This allows us to get rid of the
gen8 duplicates and also all the inlining:

add/remove: 2/0 grow/shrink: 0/21 up/down: 384/-5949 (-5565)
Function                                     old     new   delta
gen3_irq_reset                                 -     233    +233
gen3_irq_init                                  -     151    +151
i8xx_irq_postinstall                         459     442     -17
gen11_irq_postinstall                        804     744     -60
ironlake_irq_postinstall                     450     353     -97
vlv_display_irq_postinstall                  348     245    -103
i965_irq_postinstall                         378     272    -106
i915_irq_postinstall                         333     227    -106
gen8_irq_power_well_post_enable              374     240    -134
ironlake_irq_reset                           397     218    -179
vlv_display_irq_reset                        616     433    -183
i965_irq_reset                               374     180    -194
cherryview_irq_reset                         379     185    -194
i915_irq_reset                               407     209    -198
ibx_irq_reset                                332     133    -199
gen5_gt_irq_postinstall                      533     332    -201
gen8_irq_power_well_pre_disable              434     204    -230
gen8_gt_irq_postinstall                      469     196    -273
gen8_de_irq_postinstall                     1200     836    -364
gen5_gt_irq_reset                            471      76    -395
gen8_gt_irq_reset                            775      99    -676
gen8_irq_reset                              1100     333    -767
gen11_irq_reset                             1959     686   -1273
Total: Before=2259222, After=2253657, chg -0.25%

v2:
 - Make checkpatch happy with a temporary which_ (Checkpatch).
 - Reorder the arguments for the INIT macros (Ville).
 - Correctly explain when the register offsets change in the commit
   message (Ville).
 - Use more line breaks in the macro calls to make the arguments look
   a little more organized/readable.
 - Update the bloat-o-meter output (minor change only).

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/20190410235344.31199-2-paulo.r.zanoni@intel.com