Linux 5.17 compat: GENHD_FL_EXT_DEVT / GENHD_FL_NO_PART_SCAN

As of the 5.17 kernel the GENHD_FL_EXT_DEVT flag has been removed
and the GENHD_FL_NO_PART_SCAN flag renamed GENHD_FL_NO_PART. Update
zvol_alloc() to set GENHD_FL_NO_PART for the newer kernels which
is sufficient. The behavior for prior kernels remains unchanged.

1ebe2e5f ("block: remove GENHD_FL_EXT_DEVT")
46e7eac6 ("block: rename GENHD_FL_NO_PART_SCAN to GENHD_FL_NO_PART")

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #13294
Closes #13297