8047328: Improve memory usage for cards in SparsePRTEntry
Summary: Use uint16_t for cards in a SparsePRTEntry, and use an additional integer to record the current position on where to add the next card.
Reviewed-by: mgerdin, ehelin
Contributed-by: Andreas Sjoberg <andreas.sjoberg@oracle.com>, Thomas Schatzl <thomas.schatzl@oracle.com>