drm/amdkfd: Don't report local memory size

This patch sets the local memory size that is reported to userspace to 0.
This is done to make sure that userspace won't try to allocate local memory
for HSA.

As long as amdkfd doesn't support allocating local memory for HSA,
we need this patch.

Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Cc: stable@vger.kernel.org
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>