drm/amdgpu/powerplay: include asm/div64.h for do_div()

Fixes: 1e4854e9

 ("drm/amdgpu/powerplay: implement thermal control for tonga.")
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Dave Airlie <airlied@redhat.com>