ARM: HYP/non-sec/PSCI: emit DT nodes

Generate the PSCI node in the device tree.

Also add a reserve section for the "secure" code that lives in
in normal RAM, so that the kernel knows it'd better not trip on
it.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>