tu: Pass real size of prime buffers to allocator

tu: Pass real size of prime buffers to allocator

The msm driver reserves the actual DMABUF size in the memory map, while
TU can request smaller memory chunk to be allocated. This potentially
can lead to a situation when next allocation IOVA will be in the middle
of the address space which is reserved for the DMABUF. Pass the
`real_size' to TU allocator instead, so that kernel and userspace have
the same picture of memory allocations.

Cc: mesa-stable
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24861>