test(ff-a): check w3 for ffa_partition_info_get

Check that the size of the partition info descriptor is correctly
populated when calling ffa_partition_info_get.

Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
Change-Id: I56fa0e82e52c1ed35fc2ea0208d69eabc5800935
3 files changed