drm/i915: limit eDP MSO pipe only for display version 20 and below

drm/i915: limit eDP MSO pipe only for display version 20 and below

The pipes that can be used for eDP MSO are limited to pipe A (and
sometimes also pipe B) only for display version 20 and below.

Modify the function that returns the pipe mask for eDP MSO so that
these limitations only apply to version 20 and below, enabling all
pipes otherwise.

Bspec: 68923
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: James Ausmus <james.ausmus@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240404091646.165309-1-luciano.coelho@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>