qapi/vfio: Rename VfioMigrationState to Qapi*, and drop prefix

qapi/vfio: Rename VfioMigrationState to Qapi*, and drop prefix

QAPI's 'prefix' feature can make the connection between enumeration
type and its constants less than obvious.  It's best used with
restraint.

VfioMigrationState has a 'prefix' that overrides the generated
enumeration constants' prefix to QAPI_VFIO_MIGRATION_STATE.

We could simply drop 'prefix', but then the enumeration constants
would look as if they came from kernel header linux/vfio.h.

Rename the type to QapiVfioMigrationState instead, so that 'prefix' is
not needed.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240904111836.3273842-20-armbru@redhat.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>