drm/i915: Do not setup hpd without display

Now that hpd/display related calls are split from the rest in
intel_irq_init(), skip all of that in case we don't have display.

Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201106225531.920641-8-lucas.demarchi@intel.com