drm/i915: vlv: increase timeout when setting idle GPU freq

I saw punit timeouts in vlv_set_rps_idle() while running various
subtests of pm_rpm. Increasing the timeout to 100ms got rid of the
issue.

Testcase: igt/pm_rpm
Reference: https://bugs.freedesktop.org/show_bug.cgi?id=82939


Signed-off-by: Imre Deak <imre.deak@intel.com>
Tested-by: Guo Jinxian <jinxianx.guo@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>