feat(pie/por): support permission indirection and overlay

feat(pie/por): support permission indirection and overlay

Arm v8.9 introduces a series of features providing a new way to set memory
permissions. Instead of directly encoding the permissions in the page
tables the PTEs contain indexes into an array of permissions stored in
system registers, allowing greater flexibility and density of encoding.

Enable access to these features for EL2 and below, context switching the
newly added EL2 registers as appropriate. Since all of FEAT_S[12]P[IO]E
are separately discoverable we have separate build time options for
enabling them, but note that there is overlap in the registers that they
implement and the enable bit required for lower EL access.

Change the FVP platform to default to handling them as dynamic options so
the right decision can be made by the code at runtime.

Signed-off-by: Mark Brown <broonie@kernel.org>
Change-Id: Icf89e444e39e1af768739668b505661df18fb234