vfio/common: Move IOMMU agnostic helpers to a separate file

vfio/common: Move IOMMU agnostic helpers to a separate file

Move low-level iommu agnostic helpers to a separate helpers.c
file. They relate to regions, interrupts, device/region
capabilities and etc.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>