The H6 has a "secure port controller" similar to the A64/H5, but with
more ports and a different register layout. Split the platform-specific
parts out into a header, and add the missing MMIO base address.
Signed-off-by: Samuel Holland <samuel@sholland.org>
Change-Id: I3703868bc595459ecf9568b9d1605cb1be014bf5