zynqmp: Pass bl32 entry to TF-A via xilinx handoff structure

There is need to pass entry about secure OS when bl32_entry is defined.
Currently only 64bit support is added but /fit-images node have been
extended to also record if this is 32bit or 64bit secure OS. When this is
tested the code will be update to support this configuration too.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>