iommu/ipmmu-vmsa: tidyup register definitions

To support different registers memory mapping hardware easily
in the future, this patch tidies up the register definitions
as below:
 - Add comments to state to which SoCs or SoC families they apply
 - Add categories about MMU "context" and uTLB registers

No change behavior.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Joerg Roedel <jroedel@suse.de>