Update IPMMU compat strings to include SoC part number.

By specifying SoC part number in DT it becomes possible
to implement SoC specific features in the IPMMU driver.
Signed-off-by: NMagnus Damm <damm+renesas@opensource.se>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>