drm/i915/display: change pipe allocation order for discrete platforms

When big joiner is enabled, it reserves the adjacent pipe as the
secondary pipe. This happens without the user space knowing, and
subsequent attempts at using the CRTC with that pipe will fail. If the
user space does not have a coping mechanism, i.e. trying another CRTC,
this leads to a black screen.

Try to reduce the impact of the problem on discrete platforms by mapping
the CRTCs to pipes in order A, C, B, and D. If the user space reserves
CRTCs in order, this should trick it to using pipes that are more likely
to be available for and after joining.

Limit this to discrete platforms, which have four pipes, and no eDP, a
combination that should benefit the most with least drawbacks.

Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260413081609.969342-1-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

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