hyperv/stor: Refactor storvsc by applying BUS_DMA for CAM_DATA_BIO

[honzhan_microsoft.com]

Summary

This fix targets to clean the storage code with BUS_DMA interface.
In addition, this can improve the performance 1.35X ~ 2.35x for FIO on hyperv.

[sepherosa_gmail.com]

Look fine. Some minors.

sys/dev/hyperv/storvsc/hv_storvsc_drv_freebsd.c

1053

Destroy the map; though it should be no-op in this case. And the maps could also be destroyed on storvsc_detach path.

1927

Pass BUS_DMA_NOWAIT as the flag, since the code here assumes the direct running of the callback. And check the return value of bus_dmamap_load_ccb, even though it should not fail here, since no bounce pages will be needed; better safe than sorry.

[sepherosa_gmail.com]

Looks good