armv8: sec_firmware: Add support for loadables in FIT

Enable support for loadables in SEC firmware FIT image. Currently
support is added for single loadable image.

Brief description of implementation:
  Add two more address pointers (loadable_h, loadable_l) as arguments to
  sec_firmware_init() api.
  Create new api: sec_firmware_checks_copy_loadable() to check if loadables
  node is present in SEC firmware FIT image. If present, verify loadable
  image and copies it to secure DDR memory.
  Populate address pointers with secure DDR memory addresses where loadable
  is copied.

Example use-case could be trusted OS (tee.bin) as loadables node in SEC
firmware FIT image.

Signed-off-by: Sumit Garg <sumit.garg@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>