vhost-vdpa: introduce uAPI to get the number of virtqueue groups

mainline inclusion
from mainline-v5.19-rc1
commit 3ace88bd
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=3ace88bd37436abc84906312146fe5158a469142



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Follows the vDPA support for multiple address spaces, this patch
introduce uAPI for the userspace to know the number of virtqueue
groups supported by the vDPA device.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Gautam Dawar <gdawar@xilinx.com>
Message-Id: <20220330180436.24644-12-gdawar@xilinx.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Pengyuan Zhao <zhaopengyuan@hisilicon.com>