net/vdpa: Use readers/writers semaphore instead of vdpa_dev_mutex

mainline inclusion
from mainline-v5.19-rc1
commit 0078ad90
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5WXCZ
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0078ad905dc8eada34461312a0060b0904c57e2d



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Use rw_semaphore instead of mutex to control access to vdpa devices.
This can be especially beneficial in case processes poll on statistics
information.

Suggested-by: Si-Wei Liu <si-wei.liu@oracle.com>
Reviewed-by: Si-Wei Liu <si-wei.liu@oracle.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Eli Cohen <elic@nvidia.com>
Message-Id: <20220518133804.1075129-4-elic@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Pengyuan Zhao <zhaopengyuan@hisilicon.com>