iommu/ipmmu-vmsa: Write IMCTR twice

Write IMCTR both in the root device and the leaf node.

To allow access of IMCTR introduce the following function:
 - ipmmu_ctx_write_all()

While at it also rename context functions:
 - ipmmu_ctx_read() -> ipmmu_ctx_read_root()
 - ipmmu_ctx_write() -> ipmmu_ctx_write_root()

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>