refactor(optee): guard handoff logic w/ build flag

Prepare OP-TEE for environments where the Firmware Handoff (LibTL)
submodule may not be available.  Wrap all Transfer List dependent logic
in `#if TRANSFER_LIST` guards, ensuring OP-TEE can build and run without
the submodule.

This is useful for platforms or builds not integrating the firmware
handoff mechanism.

Change-Id: I701e357a8ee29d37b370c98c907d3e2795a921dd
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
1 file changed