drm/i915: Relocate intel_hpd_{enabled,hotplug}_irqs()

Move intel_hpd_{enabled,hotplug}_irqs() closes to the beginning of
the file so we can use them in more places. No functional changes.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201028213323.5423-13-ville.syrjala@linux.intel.com