drm/i915/gen9: Fix PCODE polling during SAGV disabling

drm/i915/gen9: Fix PCODE polling during SAGV disabling

According to the previous patch, it's possible atm that we call
intel_do_sagv_disable() only once during the 1ms period and time out if
that call fails. As opposed to this the spec says that we need to keep
retrying this request for a 1ms duration, so let's do this similarly to
the CDCLK change notification request.

v4-5:
- Rebased on the reply_mask, reply change.
v6:
- Remove w/s change. (Lyude)
- Rebased on the timeout_base argument change.

Cc: Lyude <cpaul@redhat.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Fixes: 656d1b89e5ff ("drm/i915/skl: Add support for the SAGV, fix underrun hangs")
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Lyude <lyude@redhat.com> (v4)
Link: http://patchwork.freedesktop.org/patch/msgid/1480955258-26311-2-git-send-email-imre.deak@intel.com