drm/i915: Move hotplug inversion logic into separate helper

drm/i915: Move hotplug inversion logic into separate helper

Use *_hpd_invert() helpers whenever possible to isolate logic specific
to hotplug inversion from common HPD setup logic to improve readability
and maintainability of the source code.

While we only define dg1_hpd_invert() here, future platforms are likely
to have different hotplug inversion needs, thus it makes sense grouping
different implementations under a common suffix.

v2: Fix coding style and prefer to use small *_hdp_invert() helpers
    instead of a generic one.

CC: Jani Nikula <jani.nikula@linux.intel.com>
CC: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220922164949.163985-1-gustavo.sousa@intel.com