Update tensor allocator for FP16 case

- With the update of ConvertU8toF16 to store F16 data in
- F16 containers instead of F32, need to update the
- function caller to have updated signatures

Signed-off-by: Jerry Ge <jerry.ge@arm.com>
Change-Id: I8568120c5e67e837eaf6ec70f8db791c4e33d48b