drm_hwcomposer: Simplify primary connector search routine

Makes it much easier to read/debug for non-c++ experts.

Drop '...' support from the 'hwc.drm.primary_display_order' property.
That means in case if no connected display fould among listed in
the property above, the routine will continue to search for connected
displays in remaining connectors by default.

Print logcat messages in case of some problems detected.

Signed-off-by: Roman Stratiienko <roman.stratiienko@globallogic.com>
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