drm/nouveau/clk: allow non-blocking for nouveau_clock_astate()

There might be some callers of nouveau_clock_astate(), and they are from
inetrrupt context. So we must ensure that this function can be atomic in
that condition. This patch adds one parameter which is subsequently passed
to nouveau_pstate_calc(). Therefore we can choose whether we want to wait
for the pstate work's completion or not.

Signed-off-by: Vince Hsu <vinceh@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>