drm/amdgpu: include pagemap.h for release_pages()

Fixes: 5ae0283e ("drm/amdgpu: Add userptr support for KFD"
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Dave Airlie <airlied@redhat.com>