drm/i915/display: convert HAS_DP20() to struct intel_display

drm/i915/display: convert HAS_DP20() to struct intel_display

Convert HAS_DP20() to struct intel_display. Do minimal drive-by
conversions to struct intel_display in the callers while at it.

v2: Rebase

Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.com> # v1
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com> # v1
Link: https://patchwork.freedesktop.org/patch/msgid/757d91d2a57052b11cbd9f4f40d836d9245ca926.1731321183.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>