Cortex-A55 has 2 64bit NEON vector units, meaning a 128bit instruction requires taking both units (and can only be issued as the first instruction in a dual issue pair). This patch models that by splitting the WriteV SchedWrite into two - the WriteVd that reads/writes only 64bit operands, and the WriteVq that read/writes 128bit registers. The A55 schedule then uses this distinction to model the WriteVq as taking both resource units, and starting a Schedule Group and WriteVd as taking one as before.
I believe this is more correct, even if it does not lead to much better performance.