Documentation: add debugfs description for hisi migration

Add a debugfs document description file to help users understand
how to use the hisilicon accelerator live migration driver's
debugfs.

Update the file paths that need to be maintained in MAINTAINERS

Signed-off-by: Longfang Liu <liulongfang@huawei.com>
Reviewed-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Link: https://lore.kernel.org/r/20241112073322.54550-5-liulongfang@huawei.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>