drm/i915: Fix the graphics frequency clamping at init and when IPS is active.

drm/i915: Fix the graphics frequency clamping at init and when IPS is active.

Part of the issue here was that Eric slipped in a debug hack for
testing the i915 IPS code before the intel_ips.c driver had landed.
This caused the driver to always use the full range of frequencies,
which is only legal when IPS tells us we have the headroom.  Once that
hack was removed, there was confusion about the driver's frequency
clamping variables: max_delay is the driver's current limit on the
highest frequency the IPS driver wants us to use, while dev_priv->fmax
is the hardware-reported limit that the IPS driver can increase up to.

Tested with IPS driver loaded or not.  Note that on Ironlake systems
without the IPS driver loaded this will result in a performance
reduction, and the inital warmup of frequency limits can impact
benchmarking on systems with IPS loaded.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
[ickle: demoted a debugging printk]
Cc: stable@kernel.org
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>