drm/i915: Jump to at least RPe on VLV when increasing the GPU frequency

If the current GPU frquency is below RPe, and we're asked to increase
it, just go directly to RPe. This should provide better performance
faster than letting the frequency trickle up in response to the up
threshold interrupts.

For now just do it for VLV, since that matches quite closely how VLV
used to operate when the rps delayed timer kept things at RPe always.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>