Support mlx5_vfio_pci style VFIO drivers (which support live migration) for
cpr-exec and cpr-transfer.

When the VFIO driver is vfio-pci, vfio_migration_query_flags() returns
-ENOTTY, so savevm_vfio_handlers is not registered or involved.

However, VFIO drivers that support live migration, such as mlx5_vfio_pci,
do support vfio_migration_query_flags(). In that case, savevm_vfio_handlers
is registered and may be used to save and load the VFIO migration stream.
This is expected for VFIO live migration, but not for cpr-exec or
cpr-transfer.

For example, the cpr-exec below never "converges".

(qemu) info migrate
Status: 		active
Time (ms): 		total=6438, setup=15, exp_down=595047
Remaining: 		6.47 MiB
RAM info:
  Throughput (Mbps): 	0.09
  Sizes: 		pagesize=4 KiB, total=0 B
  Transfers: 		transferred=71.9 KiB, remain=0 B
    Channels: 		precopy=0 B, multifd=0 B, postcopy=0 B, vfio=0 B
    Page Types: 	normal=0, zero=0
  Page Rates (pps): 	transfer=0
  Others: 		dirty_syncs=4033, downtime_bytes=32256

(qemu) info migrate
Status: 		active
Time (ms): 		total=7141, setup=15, exp_down=598507
Remaining: 		6.47 MiB
RAM info:
  Throughput (Mbps): 	0.09
  Sizes: 		pagesize=4 KiB, total=0 B
  Transfers: 		transferred=79.7 KiB, remain=0 B
    Channels: 		precopy=0 B, multifd=0 B, postcopy=0 B, vfio=0 B
    Page Types: 	normal=0, zero=0
  Page Rates (pps): 	transfer=0
  Others: 		dirty_syncs=4478, downtime_bytes=35816

(qemu) info migrate
Status: 		active
Time (ms): 		total=7682, setup=15, exp_down=595047
Remaining: 		6.47 MiB
RAM info:
  Throughput (Mbps): 	0.09
  Sizes: 		pagesize=4 KiB, total=0 B
  Transfers: 		transferred=85.7 KiB, remain=0 B
    Channels: 		precopy=0 B, multifd=0 B, postcopy=0 B, vfio=0 B
    Page Types: 	normal=0, zero=0
  Page Rates (pps): 	transfer=0
  Others: 		dirty_syncs=4820, downtime_bytes=38552


Even after migration converges with
"migrate_set_parameter downtime-limit 1000000", the target still reports
the following error:

failed (load of migration failed: Invalid argument: Failed to load vmstate version_id: 1, ret: -22)

Skip savevm_vfio_handlers for cpr-exec and cpr-transfer.

Dongli Zhang (2)
  vfio/migration: Avoid savevm_vfio_handlers for cpr-exec and cpr-transfer
  migration: Avoid inactive SaveVMHandlers in qemu_savevm_state_non_iterable()

 hw/vfio/migration.c | 8 ++++++++
 migration/savevm.c  | 6 +++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

base-commit: eea8fe61b8be8f3016e522e6af24924a0266ca95

Tested with mlx5_vfio_pci using cpr-exec and cpr-transfer.

Thank you very much!

Dongli Zhang