hisi_acc_vfio_pci: create subfunction for data reading

hisi_acc_vfio_pci: create subfunction for data reading

This patch generates the code for the operation of reading data from
the device into a sub-function.
Then, it can be called during the device status data saving phase of
the live migration process and the device status data reading function
in debugfs.
Thereby reducing the redundant code of the driver.

Signed-off-by: Longfang Liu <liulongfang@huawei.com>
Reviewed-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Link: https://lore.kernel.org/r/20241112073322.54550-3-liulongfang@huawei.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>