iommu/ipmmu-vmsa: Break out utlb parsing code

Break out the utlb parsing code and dev_data allocation into a
separate function. This is preparation for future code sharing.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Reviewed-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>