svm_migrate_init set the max svm range pages based on the KFD nodes
partition size. APU mode don't init pgmap because there is no migration.

kgd2kfd_device_init calls svm_migrate_init after KFD nodes allocation
and initialization.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>