drm/i915: Abstract the extra JSL/EHL DPLL4 power domain better

drm/i915: Abstract the extra JSL/EHL DPLL4 power domain better

Just include the JSL/EHL DPLL4 extra power domain in the dpll_info
struct. This way the same approach could be used by other platforms
as well (should the need arise), and we don't have to sprinkle
platform checks all over the place.

Note that I'm perhaps slightly abusing things here as
power_domain==0 (which is actually POWER_DOMAIN_DISPLAY_CORE) now
indicates that no extra power domain is needed. I suppose using
POWER_DOMAIN_INVALID would be more correct, but then we'd have to
sprinkle that to all the other DPLLs.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231012123522.26045-3-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>