This patch adds AArch32 support to PSCI library, as follows :
* The `psci_helpers.S` is implemented for AArch32.
* AArch32 version of internal helper function `psci_get_ns_ep_info()` is
defined.
* The PSCI Library is responsible for the Non Secure context initialization.
Hence a library interface `psci_prepare_next_non_secure_ctx()` is introduced
to enable EL3 runtime firmware to initialize the non secure context without
invoking context management library APIs.
Change-Id: I25595b0cc2dbfdf39dbf7c589b875cba33317b9d
727e5238fa