WIP: Enable support for PAGE_SIZE>4k

We now support host page sizes greater than 4k. For this to work
reliably the guest must be enlightened enough to make sharing requests
at a granule at least as big as the host. Which today means the guests
PAGE_SIZE must be equal or greater than the host.

Note that RTT tables are still allocated using the host's page size, so
most of the page will be wasted as only the first 4k are actually
delegated to the RMM. This is the main reason why this is still WIP - I
haven't yet implemented an appropriate allocator for this.

Large page sizes are also only very minimally tested, so expect bugs!

Signed-off-by: Steven Price <steven.price@arm.com>
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New patch for v7