drm/i915: Don't enable hpd detection logic from irq_postinstall()

drm/i915: Don't enable hpd detection logic from irq_postinstall()

No reason that I can see why we should enable the hpd detection logic
already during irq postinstall phase. We don't even do this on all
the platforms. We just need it before we actually enable the hotplug
interrupts in .hpd_irq_setup(), and in fact we already do it there as
well. Let's just eliminate the redundant early setup.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201028213323.5423-15-ville.syrjala@linux.intel.com
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>